According to this,

A recent study by WebmasterWorld found that an estimated 77% of all blogs on Google’s Blogspot service were spam. Similarly, AOL Hometown, had well over 80% of its results turn out to be spam. Even MSN Spaces, which as not mentioned in the report, is claimed to host an estimated ten percent of spammer Web site.

It seems as if nearly every major free blog hosting service has been either overrun or nearly overrun with spam. However, one services stands alone, a relative oasis of spam cleanliness, Automattic’s WordPress.com. Despite being just as free as its competitors and placing few restrictions on registration, WordPress.com has not endured the spam avalanche that other services have.

Though there have been spam attacks in the past, the spammers have been easily shut down and, overall, the service remains relatively free of the splogs that seem to choke up its competitors. Though paid services such as Typepad also enjoy a relatively spam-free existance, what WordPress.com does is very rare for a free service…

Those numbers are very interesting. Wonder how they affect the Technorati figures about 71 million blogs (as of now) and two new ones being created every second. Also: what is Google doing about the Blogspot problem?

Footnote: Memex runs on WordPress.