Laura at 11D has an absolutely terrific post up about how the blogosphere has changed over the last six or seven years. The upshot is that it's a lot harder to make it big in the blogosphere, while the old A-listers are burning out. Blogging more than a thousand words a day, every day, is mentally exhausting, and if you aren't getting paid for it, eventually, your life intrudes.
Back in the day, new bloggers were emerging all the time. Now it's happening much more slowly, and the old bloggers have gravitated to various professional positions. Is the new media revolution over?