Via Matthew Yglesias I've learned of a Pew study (sounds like a national study, not worldwide) that says "Eleven percent of Internet users report visiting blogs written by others. And of these blog readers, a third report posting to or commenting on the blog entries that they have read. "
That's a lot of people. Even more interesting, I think, is that the study finds that 13% of those surveyed maintain their own websites. If that's the case, then it looks to me like most people maintaining personal websites are doing so with blogs.