I've got to agree with Steve on this. Most of those products don't really seem to be “Web 2.0″ to me. I'm looking for something that looks, acts, and reacts like a desktop application would. Beyond that, it should do things that before now, would seem impossible to do inside an internet browser. YouTube, MySpace, WordPress, Flick, all those sites are merely an extention of what the web has always been about. The first things to pop up on the internet were chat rooms and bulletin boards. These are merely extensions of that initial idea. YouTube, Revver, and any other video or media file site are simply providing a community where media is shared. These have become popular primarily because before the recent past, most internet users didn't have the bandwidth to be able to consume sites like this. Personally, I think MySpace needs to be blown up. Most pages on there are impossible to decipher and have awful layouts.
Dharmesh Shah at OnStartups.com has an interesting view on the whole “Web 2.0″ thing as well.
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