What is Web 2.0?
O'Reilly -- What Is Web 2.0. Its a darn question, no one can really answer. Personally, I think that Web 2.0 really means you started your company in 2004, but it has all the latest attributes. Tim's char really sin't too bad in terms of the various ideas. He calls it a Meme Map. Some folks say it is an "attitude" toward technology rather than a definite technology itself. Personally I agree the most with that. It is about very rapid creation.
The main thing is that there are a bunch of new trends and if you don't use the keywords, then you aren't cool :-) they include a site that has Tagging, PareRank, Flogging, Bittorrent and P2P, Wikipedia, AdSense, AJAX.
Anyway the piece is a good read