I just read "Designing for the Social Web" and there's a chapter on "Collective Intelligence" (Chapter 6) http://www.amazon.com/Designing-Social-Voices-That-Matter/dp...

It doesn't get into any technical implementation details but does cover design, strategy, and issues you should consider.

You might want to browse that chapter at your favorite bookstore.

Also check out "Programming Collective Intelligence" by Oreilly. I haven't read it yet, but it is sitting on my shelf.