Stack overflow has probably been the best Q&A site around, content-wise, user-experience wise and probably every other criteria a user would care about. Good work !
Agreed. I've found it especially valuable as a bit of a teaching tool lately. I spent three years in a mind-numbing COBOL-based job, and now I'm building a PHP application to try to showcase the fact that I am more than the sum of my career, and to try to find a decent job.
Since I'm doing this in isolation, I'm trying to use StackOverflow as a surrogate mentor. When I have a question about how to do things, mostly design issues, I can usually find an existing discussion (yes Jeff, discussion) on the topic. It sucks up an awful amount of my time, but I feel like I've grown a lot professionally because of it.
About the only drawback is that it's now so popular that new questions only show up on the front page for a few minutes. So finding questions to answer - or getting your question answered is becoming harder - unless you are prepared to do a very narrow subject specific search.
One of the nice things about the early SO was it was so broad, you could see interesting questions that weren't directly in your language and read those as well.