Joseph Scott, developer at Automattic, posted that WordPress.com has recently broken 4 million total blogs. He further mentions that it took just 4 months to go from 3 million to 4 million. Assuming the rate isn’t exponential, it will just be end of December when they hit 5 million blogs. What would be even more fascinating is to know how many self-hosted blogs on WordPress are currently running. (This blog is a WordPress MU install)
WordPress seems to be no Facebook, but perhaps as projects like BuddyPress take off and people begin to virally create blogs and content with their friends it will get to that level. Where WordPress still has left to compete is with microblogging sites like Twitter – perhaps, with the large user base that they currently have we could see this happen in the near future.