I think I get what Web 2.0 is about. Wikipedia – of course – has an explanation, including attribution to O’Reilly Media in 2004 of the coining of the term and a current definition by Tim O’Reilly:
“Web 2.0 is the business revolution in the computer industry caused by the move to the internet as platform, and an attempt to understand the rules for success on that new platform. Chief among those rules is this: Build applications that harness network effects to get better the more people use them. (This is what I’ve elsewhere called ‘harnessing collective intelligence.’)“.
This excellent video Web 2.0 … the Machine is Us/ing Us concentrated my brain better than the words above. I agree with D. Weinberger who provided the link that it is a beautiful piece of work.
And for those who want some more detailed information, there is a note to the video that it has been done as a response to another Web 2.0 item (March 2006) on YouTube.