I generally defrost meat on the kitchen counter. A friend of mine suggested that this was dangerous and suggested that I defrost meat in the refrigerator. I am no biologist but it seems to me that as long as the meat doesn't get warm defrosting it on the counter should be safe. Generally, I remove the frozen items from the freezer and place them on a plate on the counter in the packaging they were frozen in. When they are mostly / completely thawed I place the meat in the refrigerator. Am I wrong and should I be defrosting in the refrigerator?

A lot of bacteria grows in the range of 40-100F (i.e. room temperature). It's definitely not recommended to defrost meat at room temperature. In fact, you are not supposed to leave meat at room temperature for more than an hour.
However, defrosting in the refrigerator can take a long time and require you to plan at least one day ahead of time. I'm not so good at this, which leads to a safe and fast solution: Defrost meat in a waterproof ziploc bag in cold water. Change the water every 30 minutes until defrosted. The water is a better conductor of heat than air, so the defrosting is quite fast and the water is cold so there's minimal safety risk.
From the USDA:

Uh, oh! You're home and forgot to defrost something for dinner. You grab a package of meat or chicken and use hot water to thaw it fast. But is this safe? What if you remembered to take food out of the freezer, but forgot and left the package on the counter all day while you were at work?
Neither of these situations are safe, and these methods of thawing lead to foodborne illness. Food must be kept at a safe temperature during "the big thaw." Foods are safe indefinitely while frozen. However, as soon as food begins to defrost and become warmer than 40 °F, any bacteria that may have been present before freezing can begin to multiply.
Foods should never be thawed or even stored on the counter, or defrosted in hot water. Food left above 40 °F (unrefrigerated) is not at a safe temperature.
Even though the center of the package may still be frozen as it thaws on the counter, the outer layer of the food is in the "Danger Zone," between 40 and 140 °F – at temperatures where bacteria multiply rapidly.
When defrosting frozen foods, it's best to plan ahead and thaw food in the refrigerator where food will remain at a safe, constant temperature – 40 °F or below.
There are three safe ways to defrost food: in the refrigerator, in cold water, and in the microwave.
Refrigerator Thawing Planning ahead is the key to this method because of the lengthy time involved. A large frozen item like a turkey requires at least a day (24 hours) for every 5 pounds of weight. Even small amounts of frozen food -- such as a pound of ground meat or boneless chicken breasts -- require a full day to thaw. When thawing foods in the refrigerator, there are several variables to take into account. Some areas of an appliance may keep the food colder than other areas. Food placed in the coldest part will require longer defrosting time. Food takes longer to thaw in a refrigerator set at 35 °F than one set at 40 °F.
After thawing in the refrigerator, ground meat and poultry should remain useable for an additional day or two before cooking; red meat, 3 to 5 days. Foods defrosted in the refrigerator can be refrozen without cooking, although there may be some loss of quality.
Cold Water Thawing
This method is faster than refrigerator thawing but requires more attention. The food must be in a leak-proof package or plastic bag. If the bag leaks, bacteria from the air or surrounding environment could be introduced into the food. Also, meat tissue can also absorb water like a sponge, resulting in a watery product.
The bag should be submerged in cold tap water, changing the water every 30 minutes so it continues to thaw. Small packages of meat or poultry – about a pound – may defrost in an hour or less. A 3- to 4-pound package may take 2 to 3 hours. For whole turkeys, estimate about 30 minutes per pound. If thawed completely, the food must be cooked immediately.
Foods thawed by the cold water method should be cooked before refreezing.

How should I get started learning to cook?

There a several types of cooking. I recommend picking one type to start learning, then branching out as you get more comfortable. This is especially helpful if you don't have access to a kitchen full of every conceivable piece cooking equipment.
Types: Baking (breads, many desserts, casseroles, pizza), Roasting/Broiling (chickens, turkeys, pot roasts, steaks), Stove-top Frying/Sauteing (stir-fry, pancakes, eggs, many italian dishes), Boiling (pasta, sauces, soups, stews), Grilling (meats, kabobs, vegetables), Smoking (fish, ham), Deep-frying (fried chicken, fish, doughnuts, corn dogs), Brining/Culturing (pickles, saurkraut, cheese).
I'd consider smoking, deep-frying, and brining/culturing to be more difficult for someone new to cooking. Grilling, Stove-top Frying, and Sauteing are fun for interactivity and flexibility. Baking is easy IF you can measure and follow directions exactly. Boiling pasta is easy, but I recommend getting some familiarity with how to spice dishes before starting soups and stews.
Depending on the type of cooking you pick, emphasis on different skill sets will be required. Skills: Cutting things up (slicing, chopping, paring), measuring ingredients (by volume, by weight, by estimate), temperature management (especially on stove top and grill), spicing/flavoring (what spices to use, in what quantities, in what combinations, at what time during cooking), evaluation (recognizing when a cooking step is complete, proper consistencies and textures for each dish), cleaning (how to wash knives, non-stick pans, clean stains), timing/serving (making sure each dish is ready for the table at nearly the same time, or that it is kept warm, cold, fresh until then), storage (keeping ingredients at their more fresh and flavorful, how to store leftovers, handling foods that can contaminate/be contaminated), shopping (creating appropriate grocery lists, maintaining a food budget, locating items in the store), and more skills I can't even think of right now.
It's a lot to learn, so don't get in over your head and try to home cook a gourmet dish for every single meal from now on.
Look to start on dishes/recipes that: That you want to eat, Don't use too many types of cooking (like braising), Don't require much more equipment than you have, Are slow paced (so you have plenty of time to figure out and prepare for the next step), Are forgiving of variation and mistakes (some dishes require precision or they fail completely), Have online video tutorials, Don't demand too much cutting (you'll speed up with practice, but no point in boring yourself).

How to Store Fresh Herbs

If you're going to store anything leafy in a plastic bag, I wrap it first in a paper towel, then in the plastic bag, so none of the leaves touch the bag. This prevents the issue where the outer leaves turn to goo. (I'm not sure what the actual biological issue is ... moisture/condensation? poor respiration?)
Don't wash it before storage, as the extra moisture will cause it to rot faster.
I think I've gotten as long as a month out of flat leaf parsley, when I buried them in the back of my crisper drawer and forgot about them. (of course, I wasn't constantly opening the bag as you would when using them, and I'm not sure exactly when I placed it in there, as I had forgotten about it)

How do you clean a cast iron skillet?

Pretty much same as all else. Wash with only a brush and hot water (while the pan is still hot) to get residue out.
Except when I have fried something that will leave a taste, like fat fish (salmon, herring or similar). Then I also use dish-washing liquid along with the brush.
Dry off on the stove after cleaning with water.
The thing to remember is that cast iron will contain small hollows which should contain fat. Otherwise everything will just burn. Feel with a finger if it "feels" fat. Otherwise pour on some cooking oil and let it simmer in low heat for a while. Swipe off excess with a paper towel.

What oil or fat to use for different purposes?

"Commonly used" depends mostly on the culture, I'd assume. There's a lot of different oils, so I've organized by use rather than try for a complete list.
Some of the ones that you might find in a "typical American" foodie's kitchen include:
For frying: something with a high smoke point : peanut, sunflower, soy, extra light olive oil
For baking (muffins & cakes): something with a mild flavor : corn, canola, "vegetable", soy
For baking (biscuits & pastry, or greasing a pan) something solid at room temp : butter, shortening, lard
For general pan cooking: olive oil (any kind), butter, anything from the "baking (muffins)" list.
For salad dressing: any nut oil, mild oil, or virgin / extra virgin olive oil
For sauces: Butter.
For finishing: something flavorful to drizzle over at the last second... odds are, it's extra virgin olive oil, but possibly sesame or a nut oil.
Now, there's regional differences -- in the south, it's pretty common to save your bacon grease for cooking and to use shortening for frying. Lard's still popular in hispanic (and likely other) cuisine, schmaltz (rendered poultry fat) is used in both Jewish and French cooking. Ghee (similar to clarified butter), is used Indian cuisine ... and the list goes on.
If you're looking for a 'must keep on hand' list -- a mild oil, extra virgin olive oil and butter will get you through most anything. Add shortening if you like baking, and sesame oil if you like to cook asian food, and you'll be prepared for most anything.

When you cook with wine or spirits, when does the alcohol cook away? Obviously high temperatures will do it, but how low of temperatures will work? Also, does it vary by the type of alcohol?

Preparation Method and Percent of Alcohol Retained

• alcohol added to boiling liquid & removed from heat: 85%
• alcohol flamed: 75%
• no heat, stored overnight: 70%
• baked, 25 minutes, alcohol not stirred into mixture: 45%
• baked/simmered, alcohol stirred into mixture:
  
  • 15 minutes - 40%
  • 30 minutes - 35%
  • 1 hour - 25%
  • 1.5 hours - 20%
  • 2 hours - 10%
  • 2.5 hours - 5%

If I leave fully-cooked food (particularly meat) out at warm temperature - say on the counter or in a crock pot that's been turned off - how long will it stay safe to eat?

Storing Leftovers
One of the most common causes of foodborne illness is improper cooling of cooked foods. Because bacteria are everywhere, even after food is cooked to a safe internal temperature, they can be reintroduced to the food and then reproduce. For this reason leftovers must be put in shallow containers for quick cooling and refrigerated within 2 hours.

You'll find similar statements from government agencies around the world. The safe limit for raw or cooked food is 2 hours in the danger zone (40-140° F or 4.4-60° C).
If you're a restaurant owner or cook, you must follow this rule, hold hot foods above 60° C and quick-cool other foods before refrigerating. If you are not working in a professional capacity then you are not legally required to follow it, but if you are serving guests then it would be irresponsible (and possibly actionable, if someone gets sick) to do otherwise.
If you're an individual serving only yourself, then take whatever liberties and break whatever rules you want; it's your food, and your body. But there's no table or chart anyone can give you; there's no single specific point at which a food transitions from "not entirely safe" to "probably will kill you" because it depends entirely on the food, the environment, your immune system, and a plethora of other variables. The rule is 2 hours, period; any longer and there is some non-trivial risk to your health.
Some hints, tips, and warnings:

• The 2-hour rule is a conservative estimate with a safety margin. Don't ask what that margin is. It's like asking what the "real" speed limit is on a posted road; you might know from experience, but it could change depending on circumstances and exceeding it by any amount means you take your chances and accept the risks.
• Don't put large, hot items (such as an entire pot of soup or chili) directly into the fridge. The residual heat will warm up and potentially spoil other items in the refrigerator.
• To quickly cool large cooked items, use an ice-water bath and/or divide them into small containers. (Note: Don't use an ice-water bath for cast iron.)
• Don't assume that re-cooking an improperly-stored item will make it safe. Most bacteria produce protein toxins, which are actually the primary agents responsible for food poisoning, and several of these toxins are heat-resistant. Cooking will not kill or inactivate these toxins and eating the re-cooked food will still make you sick.
• Don't assume that cooking "kills everything" and that a cooked food or cooking surface is absolutely sterile. Cooking kills enough to make the food safe to eat, but some organisms - such as bacterial spores from bacillus and clostridium - can survive the cooking process and immediately start producing more bacteria. Sous-vide bags, crock pots, etc. are not safe environments for cooked food in the temperature danger zone.

How do I know if food left at room temperature is still safe to eat?

When in Doubt, Throw it Out!

You cannot see or smell bacterial contamination. Mold that appears to be growing only on the surface may grow invisible roots into softer foods. Do not rely on a visual inspection or "smell test" to tell you whether or not a food is safe.

The Danger Zone

• Potentially hazardous food that stays in the temperature "danger zone", 40-140 °F (4-60 °C), for more than 2 hours should be discarded.^*
• Potentially hazardous foods are those foods that spoil most easily, such as unshelled eggs, raw meats, fish, shell fish, dairy products, almost all cooked foods.
• This time is cumulative, so it includes time bringing the food home from the grocery store, time before cooking, time after cooking, and so on. The reason is that while cooking may destroy bacteria or other pathogens, it doesn't always destroy the toxins that they have produced.
• So in general, regarding perishable foods like meat, most dairy, unshelled eggs and shell eggs (in the US), cooked casseroles, and so on: if the food (or its perishable components) have been at room temperature for more than two hours, you should discard that food.
• To avoid the danger zone, keep cooked food hot until ready to eat, then refrigerate immediately. Separate large items into smaller containers to help them to cool more quickly. If you’re defrosting something, do it in the fridge or under cold running water.

Why does cooking not completely "reset the clock"?

• Some bacteria leave behind harmful protein toxins that cannot be "killed" (denatured) by cooking. Cooking food is only effective against live organisms, not their toxic waste products. Spoiled food cannot be cooked back to safety and must be discarded.
• Cooking is pasteurization, not sterilization. Pasteurization means killing most microbes, so as to render the food safe for human consumption. Sterilization methods (e.g. pressure-canning and irradiation) are the only safe methods for longer-term room-temperature storage. Otherwise, the danger zone rules always apply.
• Even sterilized food can only remain sterile under an airtight seal, e.g. when properly canned or vacuum-sealed. Once it is opened, it is no longer sterile. Air contains countless bacteria and molds, and their spores, which will readily re-colonize any suitable environment they encounter. Cooked food tends to be an ideal medium for growth.

Regulation and Risks

Follow the guidelines set out by reputable regulatory agencies, especially when serving others. Local organizations include:

• FDA Food Code (USDA)
• CFIA (Canada)
• Food Standards Agency (UK)

Other regulatory sources apply in other parts of the word, but major food safety organizations usually agree in essence (if not in complete detail) on most issues.
Failure to follow reputable guidelines is irresponsible if you are serving guests, and failure to follow your specific local codes is likely to be illegal if you are serving customers.
Health codes tend to be very conservative, to fully protect the community. You have the right to take risks on yourself by ignoring their recommendations, but please do not risk the safety of others.

Again, When in Doubt...

Once again, if you suspect spoilage or contamination, please, throw it out.
_{* Note: this is the FDA's rule. Other agencies may have variations on it. Additionally, government agencies generally make very conservative recommendations - they're trying to make sure that no one who follows the rules gets sick. Breaking the rules means maybe taking on some risk. That's up to you - just remember, eventually someone gets unlucky, and food poisoning is not fun.}

Helpful Resources

• Wikipedia: Food Safety
• USDA Fact Sheet
• Still Tasty - has information on storage methods/times for almost every food.

Further Reading/Frequently Asked

• Why is it dangerous to eat meat which has been left out and then cooked?
• How long can I store a food in the pantry, refrigerator, or freezer?
• What Do I Need To Know About Temperature and Food Safety?
• Is there a problem with defrosting meat on the counter?
• How long can cooked food be safely stored at room/warm temperature?
• Is it safe to cook a steak that was left out (raw) for 7 hours?
• How long can eggs be unrefrigerated before becoming unsafe to eat?
• Should I refrigerate eggs?

How long can I store a food in the pantry, refrigerator, or freezer?

The shelf-life is the amount of time a food can be stored before it is considered unsuitable for use. It may be unsuitable due to quality degradation (no longer tasty) or food safety (risk of food poisoning). [1]
As far as food safety goes, food stored frozen at 0°F (-18°C) or below is remains safe forever; only quality degrades over time. [2]. Thus the freezer-storage times below are entirely about quality.
If your freezer is set at a temperature higher than -18°C (three-star setting), these times may not apply. Especially the safe storage time in one-star freezers (-6°C) is much reduced.
The times all assume proper storage. Freezers 0°F or below, refrigerators 40°F (4°C) or below. [3] Cans should be stored in a cool, dry place, below 85°F (30°C) [4].
The tables given here assume proper storage. Food which requires refrigeration is considered unsafe if left for over two hours at temperatures between 41–135°F (5–57°C) [5].

The Tables

Regardless of the table below, if a food shows signs of spoilage (including mold, with some exceptions described below), its past its shelf-life. Note that the lack of spoilage does not imply safety.

Uncooked Proteins

Item              Fridge                 Freezer                    Sources
----              ------                 -------                    -------
Ground (meat,     1–2 days               3–4  months                [KC]
poultry)
Non-ground        3–5 days               steaks: 6–12 months        [KC]
meat                                     chops:  4–6  months   
                                         roasts: 4–12 months   
Poultry           1–2 days               whole: 12 months           [KC]
                                         pieces: 9 months
Eggs              in shell: 3–5 weeks    in shell: not recommended  [KC]
                  separated: 2–4 days    whites: 12 months
                                         yolks: not recommended
Bacon             1 week                 1 month                    [CFG]
tofu              1 week                 5 months                   [CFG]
fish              1–2 days               lean:  4–8 months          [CFG]
                                         fatty: 2–3 months

Cooked proteins

Item              Fridge             Freezer               Sources
----              ------             -------               -------
luncheon meat     opened:   1 week   1–2 months            [KC]
                  unopened: 2 weeks
cooked meat and   3–4 days           2–6 months            [KC]
poultry
cooked fish       3–4 days           1–2 months            [CFG]
hard boiled eggs  1 week             not recommended       [KC]
hard sausage      2–3 weeks          1–2 months            [CFG]

Dairy

Item              Fridge                Freezer               Sources
----              ------                -------               -------
butter            1–3 months            6–9 months            [CFG]
hard cheeses      opened: 3–4 weeks     6 months              [CFG]
                  unopened: 6 months
soft cheeses      1 week                6 months              [CFG]
cream cheese      2 weeks               not recommended       [CFG]

Sauces

Item              Fridge                 Freezer               Sources
----              ------                 -------               -------
mayo              commercial: 2 months   not recommended       [CFG]
                  home-made: see below
gravy, broth      3–4 days               2–3 months            [CFG]

For home-made mayo, there don't seem to be official shelf-life estimates. Seasoned Advice has a question on this, Making "long(er)-life" homemade mayonnaise.

Vegetables

Freezer times are given for cooked or blanched, then frozen. Generally, this is required, otherwise enzymatic degradation will occur. See "Where can I go for details on a specific food?" for where to find specific steps for each vegetable.
Refrigerator and shelf times are for storage raw.
If a column is -, it means that storage type is not recommended. "Ripe" means "until ripe".

Item                Shelf         Fridge       Freezer                 Sources
----                -----         ------       -------                 -------
Asparagus           -             3–4 days     8 months                FK
Green beans         -             3–4 days     8 months                FK
Beets               1 day         7–10 days    6–8 months              FK
Cabbage             -             1–2 weeks    10–12 months            FK
Carrots             -             3 weeks      10–12 months            FK
Celery              -             1–2 weeks    10–12 months            FK
Garlic              1 month       1–2 weeks    1 month                 FK
Herbs (fresh)       -             7–10 days    1–2 months              FK
Lettuce (iceberg)   -             1–2 weeks    -                       FK
Lettuce (leaf)      -             3–7 days     -                       FK
Mushrooms           -             2–3 days     10–12 months            FK
Onions, non-sweet   2–3 months    2–3 months   10–12 months            ST
Onions, sweet       1–2 months    1–2 months   10–12 months            ST
Peppers             -             4–5 days     6–8 months              FK
Potatoes            1–2 months    1–2 weeks    mashed: 10–12 months    FK
Squash, summer      -             4–5 days     10–12 months            FK
Squash, winter      1 week        2 weeks      10–12 months            FK
Tomatoes            ripe          2–3 days     2 months                FK

Fruits

Many fruits must be at least partially cooked (blanched) before freezing in order to deactivate enzymes that would otherwise degrade quality while in storage. Some are best frozen packed in acid (lemon juice or citric acid) and/or syrup. See "Where can I go for details on a specific food?" for where to find specific steps for each fruit.
If a column is -, it means that storage type is not recommended. "Ripe" means "until ripe".

Item              Shelf      Fridge                 Freezer               Sources
----              -----      ------                 -------               -------
apples            1–2 days   1–3 weeks              cooked: 8 months      FSG, FK
apricots          ripe       2–3 days               -                     FK
bananas           ripe       1–2 days*              peeled: 1 month       FK
berries           -          1–2 days               4 months              FSG, FK
citrus fruit      10 days    3 weeks                -                     FSG
grapes            1 day      1 week                 1 month               FK
juice             -          6 days                 8 months              FSG
melons            1–2 days   1 week                 balls: 1 month        FSG, FK

generally:                   3-5 days

*: bananas stored in the fridge will blacken.

Cooked dishes

Generally 3–4 days in the fridge. This includes pizza, soups, stews, casseroles, pies, and quiche [KC]. Some salads get a fifth day [CFG]. Freezer time is generally under three months.

Shelf-stable until opened

Item                                    Unopened      Opened, in fridge    Source
----                                    --------      -----------------    ------
Commercially canned, low-acid           2–5 years     3–4 days             [CFG]
(meat, poultry, fish, soups, stews
 vegetables)
Commercially canned, high-acid          12–18 months  5–7 days             [CFG]
Olives                                  12–18 months  2 weeks              [FK]
jam, jelly,                             1 year        6 months             [FK]
preserves
shortening (Crisco)                     8 months      3 months             [FK]

Pantry (not refrigerated even after opening)

Item                Shelf life              opened (if different)    source
----                ----------              ---------------------    ------
Baking powder       18 months                                        [FSG]
Baking soda         2 years                                          [FSG]
beans (dry)         1 year                                           [FK]
Bouillon            1 year                                           [FSG]
cornstarch          18 months                                        [FK]
extracts            3 years                                          [FK]
flour               white: 6–12 months                               [FK]
                    wheat: 1 month
herbs (dry)         1–2 years               1 year                   [FK]
honey               1 year                                           [FK]
pasty (dry)         2 years                                          [FSG]
egg noodles (dry)   6 months                                         [FSG]
rice (dry)          white:    2 years                                [FSG]
                    brown:    6–12 months
                    flavored: 6 months
vegetable oil       6 months                1–3 months               [FSG]
vinegar             2 years                 12 months                [FSG]

General tips for storing foods

How do I freeze fruits and vegetables?

Fruit. Ripe (but not overripe) fruit should be used. Wash them, and sort according to size. Working in small batches, remove pits, seeds, and blemishes. For fruits that turn brown, apply ascorbic acid or sugar and citric acid. Most fruits benefit from packing in dry sugar or a sugar syrup. Small, whole fruits (e.g., berries) can be spread on a tray and individually frozen, then packed in a freezer bag or other airtight container.
Vegetables. Most vegetables need blanching. To blanch, immerse in boiling water over high heat or steam over rapidly boiling water (steam). After blanching, transfer to ice bath for the same amount of time as blanched. Drain and dry. Freeze either by packing in a freezer bag with as much air as possible removed, or by allowing to freeze on a tray, then putting in a bag or other container.
General guideline is 8–12 months for best quality.
The above is a very quick summary of Iowa State University's Preserve the Taste of Summer: Freezing: Fruits and Vegetables. The five-page document includes full details on over forty fruits and vegetables. Feel free to ask here on Seasoned Advice if that guide doesn't answer your question.

What about mold?

Some foods are expected to have mold in them (e.g., P. roqueforti in Roquefort cheese). Unexpected mold, however, is something to be concerned about. Mold can grow even on refrigerated foods, and even those high enough in salt or sugar to deter bacteria. Some molds produce mycotoxins. Mold growth can be minimized by cleaning the refrigerator every few months (use a mixture of 1 tablespoon of baking soda per quart of water, then rinse with plain water, then dry), by keeping dishcloths, sponges, mops, etc. clean and fresh-smelling; and keeping indoor humidity levels under 40%.
In general, the visible surface mold on a food is only a small part of the actual mold growth. For most foods, any visible unexpected mold growth means you should discard the entire item. There are several exceptions:

Hard salami, dry-cured     Scrub mold off surface.
country hams

Hard cheese                Cut at least 1 inch around and below mold spot,
                           do not cut through mold.

Cabbage, bell peppers,     Cut at least 1 inch around and below mold spot,
carrots                    do not cut through mold.

Everything else, including soft or shredded cheese, soft fruits and vegetables, bread, peanut butter, jams and jellies, sour cream, yogurt, luncheon meats, casseroles, and cooked pasta should be discarded.
All this information comes from the USDA FS&IS's Molds on Food: Are They Dangerous? fact sheet.

Where can I go for details on a specific food?

The web site StillTasty maintains a comprehensive list of food storage times, notes, and procedures for a wide variety of food items. They draw information from a variety of reputable sources and should probably be the first place you check.
Another good source of information is the Food Marketing Institute's Food Keeper. This is also a searchable database of foods.
Finally, if neither of those two references answer your question, you're at the right web site. Please ask here on Seasoned Advice.

Bibliography

• [CFG]: USDA FS&IS Cooking for Groups: A Volunteer's Guide to Food Safety
• [KC]: USDA FS&IS Kitchen Companion: Your Safe Food Handbook. February 2008.
• [FK]: Food Marketing Institute, Food Keeper
• [FSG]: Julie Garden-Robinson, North Dakota State University, FN-579 Food Storage Guide
• [ST]: StillTasty.com, Keep It or Toss It?

Note

This is a work-in-progress. I still need to finish adding information to it. Also, this answer is a community wiki, please feel free to improve it.