You can break down Web 2.0 customers into a fuzzy hierarchy:
1. Creators who create an original work. Examples include a reporter at the New York Times, a podcaster, a blogger who is writing original content, or the author of Harry Potter.
2. Linkers who annotate the work of Creators. Examples include a blogger who mostly links to other content or a del.icio.us user who publishes the RSS feed of his bookmarks.
3. Commenters who comment on the Creators and Linkers work. Examples include anyone who writes a comment on a blog.
4. Surfers who consume the output of Creators, Linkers, and Commenters. Anytime you read someones blog, you are a Surfer.
How many more Linkers are there than Creators? How many more Commenters are there than Linkers? Do you get 10x more customers at each level of this hierarchy? My guess is that the number of customers grows geometrically as you move down each level of the hierarchy.