James Dellow at ChiefTech points to a great video that explains Web2.0: Web 2.0: The Movie:
This great little short video, titled "Web 2.0 ... The Machine is Us/ing Us", explains the difference between traditional content (including "Web 1.0") and Web 2.0. Thank you to Michael Wesch, an anthropologist at Kansas State University, for putting it together.
It doesn't get into all the nitty gritty - it does a flyover of what this all means, set to a nice soundtrack.