The correct answer is, of course, that Web 2.0 is a little of all of those definitions (as one commenter offers, the idea of trying for a definition at all may be misplaced, a la Wittgenstein). My own definition, if it could be called that, identifies the salient features of a network (like this) found in the new internet technologies and offers four standards of good practice: openness, diversity, autonomy, and connectivity. Of course, these are rough approximations too. Don't forget to read the comments; lots of great ideas. Via Assorted Stuff.