When Time Magazine picked "You" as their Person of the Year for 2006, they cemented the idea that Web 2.0 is about "user generated content" -- and that Wikipedia, YouTube, and MySpace are the heart of the Web 2.0 revolution. The true story is so much more complex than that. The content that users contribute explicitly to Web 2.0 sites is the small fraction that is visible above the surface. 80% of