Technorati, who measures that sort of thing, says there are 70 million blogs out there, with 120,000 new ones being added every day. Technorati doesn't index big sites like Twitter or Facebook, if you consider them blogs, so there are millions more.
Implications - Technorati is special because it is able to search for blogs that have been unused for years or made for spam and delete them to create new space. Dave Sifry is the founder of Technorati, which started up in 2004. The company would track the activity of the blogosphere every six months.