How is it that questions posted to the Stack Overflow show up as #1 in Google search results just minutes after being submitted? What SEO practices are being used to generate this sort of up-to-the-minute accuracy?

I've done a LOT of experimenting with Google rankings. I know I posted a question to one of the stack exchanges sites and was surprised that the question hit my Google Alerts (http://www.google.com/alerts) withing 24 hours.

Google always ranks Wikipedia and Stack Overflow really highly. I believe there are two reasons for this.

1) Neither of these two sites "sell" anything. They are informational. Google knows that any Wikipedia page has no hidden agenda. Anyone who visits one of their pages will find what they are looking for, probably more than they are looking for.

2) Both of these sites are constantly being updated and rely on content created by intelligent users who aren't selling anything. Again, 99% of answers really shed light on myriad topics.