We are currently seeing about 30,000 - 40,000 new weblogs being created each day, depending on the day. Compared to the past, this is well over double the rate of change in October, when there were about 15,000 new weblogs created each day. The remarkable growth over the past 3 months can be attributed to the increase in new, mainstream services such as MSN Spaces, and in increases of use of services like Blogger, AOL Journals, and LiveJournal. In addition, services outside the United States have been taking off, including a number of media sites promoting blogging, such as Le Monde in France.Link
There is a dark underbelly to these numbers, however: Part of the growth of new weblogs created each day is due to an increase in spam blogs - fake blogs that are created by robots in order to foster link farms, attempted search engine optimization, or drive traffic through to advertising or affiliate sites.