I have watched a rather short video by Brooke Aker (CEO of Expert System) at ZDNet Videos, on Semantic Search: the promise of a Web 3.0 based on semantic (Natural Language Processing) technologies, entitled "Web 3.0 Semantic Search".
Apart from selling the watcher the promise of a new boost to productivity, Brooke makes a very simple description of the main difference between Web 1.0 and Web 2.0. The idea is that Web 1.0 is a one producer/mass consumer of information world, while Web 2.0 is a mass producer-mass consumer of information world. It is very simple to tell, and to understand.
Go watch the video, it is only 3:42 minutes long. Worth watching popular videos at the bottom of the page.