Amazon sent me an invitation to their new service called Askville this morning. Essentially Askville is a social question and answer space that uses questions as the basis for social interaction and discussions. I like that there are lots of people asking totally free-form questions and getting lots of answers -- I think I'd probably ask questions about good restaurants, places to stay, etc. when traveling to a city I was unfamiliar with just to see what locals or people that have been there before would say.
There is some system of points and levels and "quest coins," but I didn't spend much time reading about any of it -- you can find details here in the FAQ. I have to guess that Amazon may use some of this content to link through to products that they are selling to provide even more valuable product information and insight.
Check it out.