At last, I've made my mind about what Web 2.0 really is!
Point in time where the powers-that-be discover that a significant and increasing number of people are effectively using the internet in their daily life.
Corollary, here is my definition of Web 1.0: Point in time preceding Bubble 1.0, during the development of the internet, where the powers-that-be discover the web for the first time while investors' pockets are full.
By Bubble 1.0, I mean the moment when investors —who didn't necessarily (or even tried to) understand what the heck this internet thing could possibly be used for— discover that nobody is using it, besides the geeks they funded. Had the notion of tag cloud existed back in time, the words ROI and business model would have popped up at size 72pt+ at the beginning of 2000.
Bonus, here is my definition of Bubble 2.0: correction phase, following Web 2.0, where the powers-that-be who discovered that lots of people are using the internet without really grasping why they use it, are asked by their investors to go play elsewhere.
Double bonus, my definition of Web 3.0: phase when those who brag about being "web enabled" or their SOA capabilities are looked down as if they'd just discovered the phone. Note that if you foolishly talk about Web 2.0 in front of a geek, you'll get a taste of that condescending look already ;-).
You'll note that I didn't make any reference about technology in those definitions. There are no new technologies in Web 2.0. You'll also note that I don't refer to specific concept such as collaboration, which to me is simply a consequence of the democratization of the internet, an effect of mass inducing a percolation of personal behaviors in a social space. To sum it up, we're talking about the temporal discovery of the social development of the internet. This is where the buzzword Web 2.0 starts to have substance.