In this recent article from Information Week, it says:
"A new blog is created every second and the phenomenon has grown 60 times larger than it was three years ago, according to Dave Sifry at Technorati.
In "State of the Blogosphere," published most recently on Monday, Sifry said there are about 27.2 million blogs and 75,000 new ones created each day. At that rate, the blogosphere doubles about every 5.5 months, with about 1.2 million new posts daily, or 50,000 an hour."
Read the article here