According to Jeff Atwood:
Stackoverflow is sort of like the anti-experts-exchange (minus the nausea-inducing sleaze and quasi-legal search engine gaming) meets wikipedia meets programming reddit. It is by programmers, for programmers, with the ultimate intent of collectively increasing the sum total of good programming knowledge in the world. No matter what programming language you use, or what operating system you call home. Better programming is our goal.
According to Joel Spolsky:
There is nothing there yet, apart from a podcast. But, with their combined talents and high profiles, it could be a great resource for software developers. I will be watching with interest.