If you're looking for the real definition of the term Web 2.0 I suggest you visit a page from a O'Reilly Media site. I must warn you though, Tim O'Reilly, who for simplicity sake I'll say is the inventor of the Web 2.0 term, can't even explain it without writing at least 6 pages of text, and oh yeah, a few diagrams.
My definition of Web 2.0:
A model in which the main objective is to create a website that intrinsically provides no value unless a multitude of users have signed up and contribute their own effort and knowledge to the site. The model also requires the site to look 'cool' and do 'cool' things and must be provided to users at no cost. The final piece of the puzzle is to slap ads on the site and claim that 'the game has changed'.
Q: Does Web 2.0 really matter? A: No
Q: Why isn't Web 2.0 just a different internet business model? A: Because it wouldn't be as cool
I think the most important thing to remember is that any 'Web 2.0' site that is successful, has done so because it has gone mainstream. And if it has gone mainstream then the majority of users won't know (or care) what the hell Web 2.0 is...honestly, they won't give a shit. The reason we have Web 2.0 is (1) more people on the internet (2) faster computers (3) more bandwidth.
The most sickening part is I've been hearing people throw Web 3.0 around now...the audacity!