Web 2.0 isn't a version. For O'Reilly it's a marketing term used to sell books, blogs, magazines, and conferences. For everyone else who took part in the infamous definition discussions it was a helpful prompt for talking about where the web is and where it's going. Really, though, Web 2.0 just signifies whatever we're doing with the web right now that is exciting and cool and different from how we used the web 5, 10 or 15 years ago.
Here's an excerpt from a piece I wrote at ReadWriteWeb last year entitled "There is No Web 3.0, There is No Web 2.0 - There is Just the Web" ...
"[The] versioning of the web is silly. Web 1.0, 2.0, or 3.0 is all really just whatever cool new thing we're using the web to accomplish /right now/.
...
Web 2.0 and Web 3.0 -- they don't really exist. They're just arbitrary numbers assigned to something that doesn't really have versions. But the discussion that those terms have prompted have been helpful, I think, in figuring out where the web is going and how we're going to get there; and that's what is important."
Link: http://www.readwriteweb.com/archives/there_is_no_web_30_ther...
So let's dispense with the "Web 2.0 is over, onto the next version!" meme and instead just focus on what the web is, what we can do with it now, and where we can take it in the future. </rant>