David Sifry presents the State of the Blogosphere, 2005 starting with the growth of blogs. According to Technorati statistics:

• The blogosphere is doubling in size about every 5 months
• 35-40,000 new blogs are created every day. That's a new blog every 2.2 seconds.

He also adds, however:

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. We have been battling the spam situation in a significant way for about 2 months - prior to January, spam wasn't much of an issue. All of these charts reflect Technorati's databases after spam blogs have been removed, and we feel that we've been able to capture and identify most of the spam out there, but one should note that there is definitely blog spam that we don't catch (tell us if you see spam in the index!). I'd estimate that we currently catch about 90% of spam and remove it from the index, and notify the blog hosting operators. Most of this fake blog spam comes from hosted services or from specific IP addresses. One of the results of the extremely productive Spam Squashing Summit of a few weeks ago is the increased collaboration between services in order to report and combat this spam. Right now, about 20% of the aggregate pings Technorati receives are from spam blogs, so you won't see that in these numbers - these statistics show only "cleaned" data.