Google may be sticking its toes into Affiliate Programs. They apparently are calling these CPA (Cost Per Action) ads, but what that means is that publishers get paid not for clicks but for some specific action at an advertiser's site: buying something, providing information, whatever. That's an Affiliate Program, Google is just naming it something else.
Interestingly, this comes at the same time that eBay is murmuring about its own affiliate style thingy. What they intend to do is let sites like this run ads pointing at appropriate auctions. For example, we might run ads for auctions related to computer hardware, and would get paid if someone reading here clicked through and won the auction (or purchased a Buy It Now item).
I hope the program becomes as successful as the adsense itself! Amen!