Stackoverflow.com is a soon-to-be-released developer community website from Jeff Atwood and Joel Spolsky. It is an evolution of existing sites in the genre, adding reddit and wiki type features to the traditional forum style site.
The technology stack it uses is nearly identical to my current personal project: Asp.Net MVC, jQuery, Linq-to-sql, sql 2005. The truly fascinating thing about stackoverflow.com is the buzz. There are already thousands of users on the private beta. I predict, and Joel Spolsky concurrs, that when it goes live it will be huge. Not because its a great site, which it is, but because of the spectacular Atwood/Spolsky marketing machine. These two gentleman have enourmous credibility in the developer community and it shows in the early success of their new joint venture. It is a perfect demonstration of how online reputation is an asset and how to leverage that asset into a business that makes money.
My final prediction is that their server will crash in the first week of go-live. It will be karma's revenge for making fun of twitter.