StackOverflow is genius. Two respected and popular software development bloggers putting their audiences to work to make a better mutual-aid site for programmers.
Incredibly this seems something that no-one else has done. Most places for programmers to help each other are based on pretty lousy generic discussion forum software and plastered with adverts.
Joel Spolsky and Jeff Atwood have rethought the whole thing and made a far far better service.
It reminds me of a post I wrote about Behance, Design Outpost, Tribe and other more specialized YASNS and markets. There's a huge largely untapped opportunity ... to take YASNS away from generic people-collecting sites and make them useful vehicles for communities to work together. In my fantasy I talked about putting diverse but complementary communities together. But StackOverflow reminds us that there's also plenty of room just to take a rather tired and ineffective genre of community site and make it a hell of a lot better.