I liked Nivi's post working through the Web 2.0 customers. I think he missed a key point though, which is that some of the most interested work created is done by people building off of the work of others before them. In his categorization my only choices are "linkers" or "commenters". I was going to suggest adding a category for "remixers", but I think the right thing to do is fix the "creator" category to capture these folks:
Creators who create an work, either 'original' or derived from one or more previous works. Examples include a reporter at the New York Times, a podcaster, a blogger who is writing original content, or the author of Harry Potter.