A Web 2.0 Tour for the Enterprise may sound like it is explaining RSS and Wiki to Captain Picard, but is in fact a useful introduction to Web 2.0.
It also links to the article What is Web 2.0 by Tim O’Reilly, which is another very handy article to explain the basics of Web 2.0.
Squidoo has a reading list for a Library 2.0 course by the ALA which includes an article introducing Web 2.0 (with links to more articles, books and examples). It also has a number of definitions for Library 2.0, mostly from various Blogs, which gives it a nice web 2.0 feel! There follows a list (with summaries) of articles on Library 2.0, (far too many for me to talk about here – go and look!), flickr images, podcasts, you name it. A very useful resource for learning about Web and Library 2.0, and seeing things in action.