This thing - this sensation - we call Web 2.0 has been given hundreds of definitions. I'd rather liken it to pornography. I can't tell you exactly what it is, but I know it when I see it.
What we Know About Web2.0
It's got something something to do with community and sharing. The Web was a pretty stale tasting place just before every other popular page was as dynamic and interactive as a video game.
It's got something to do with getting a "zombie bite" on your Facebook profile from a friend.
It feels more like driving an experience than being pitched to.
It can only be explained by its whole and not the sum of its parts.