TechCrunch has a post that touches XuQa’s monetization strategy. The social networking site has developed a mini-economy centered on earning peanuts. One way that users can earn peanuts is to complete CPA offers.
While I was a part of Kiwibox, we made a big push to allow users to earn “KiwiPoints” by completing offers and surveys. I was amazed at how well targeted offers could perform. Another site with a great implementation of this strategy is NeoPets. They were one of the first big communities to do a great job monetizing users through CPA offers. I have heard from survey vendors that they can just unleash huge amounts of users to complete surveys in exchange for points.

From my time at Kiwibox, I have some experience launching programs to reward users for completing offers. If you are interested in getting some help with setting up a similar program on your site, you can contact me at paul@monetizetraffic.com.