On a related question, I'm intrigued as to how this kind of market is different from Apple's App Store[1]. I know Google expenses its AdSense partner cost as traffic acquisition cost[2], but what about them makes the IRS/SEC view them differently?
[1] http://tech.fortune.cnn.com/2010/06/23/app-store-1-of-apples... [2] http://news.ycombinator.com/item?id=1792921