You may seen this thrown around now and again. There are lots of definitions for it, and a lot of buzz some merited some not. As I see it the key defining attribute of web 2.0 is 'user generated content.' Youtube and Myspace are perfect examples of this, where developers create the context and infrastructure and site visitors create the content. While is it is context and infrastructure that make the site work, it is content that keep people coming back again and again. Simple isn't it?