conclusion: Tim O'Reilly, the man credited with popularizing the term Web 2.0, doesn't actually believe it exists. For O'Reilly, there is just the web right now. 1.0, 2.0, 3.0 -- it's all the same ever-changing web.
One web to rule them all,
One web to find them,
One web to bring them all, and
In the present bind them.
(poetic frame from J.R.R. Tolkein's Lord of the Rings)
The Web need not be new and different. "[W]hat matters are the discussions" (Catone, There is No Web 3.0..., ¶8, 2008.04.24, after O'Reilly, days earlier).
Bob Rankin explains what makes web 2.0 different from web 1.0, and speculates on what web 3.0 might be like. Concise and clear, ideal for people asking this question for the first time.
"The first International Open Access Week is scheduled to take place October 19-23; it is an opportunity to broaden awareness and understanding of Open Access to research......."