Briefly, there's a conference happening at the moment in San Francisco called Web 2.0; There's this guy called Tim O'Reilly who publishes computery books, and has visions; Many people say that Flickr is a Web 2.0 application.
I particularly enjoy this summary of what this Web 2.0 thing means from a lady called Tory, on a blog post by 37 Signals.
I know exactly what web 2.0 is:
* oversized fonts
* pastel colors
* featureless “user experiences”
* overly friendly and self-important copy
Basically it’s 1998 with less money and more metrosexuals.