Would you believe that about a third of blogs are spam? At least those are the numbers for Wordpress, according to Matt Mullenweg, the blogging platform's founder. But think about how many spam blogs there are out there. You'll find them in pingbacks, search results, and linking through spam comments. Is it hard to believe that about a third of blogs out there really are spam?
What's important to note here, though, is the fact that Wordpress has been able to protect its brand equity in spite of all these spam blogs. I think that's really testimony to the effectiveness of Wordpress' spam-blocking tools, like askimet.
But looking at the larger picture, spam blogs have managed to infiltrate other arenas around the Web. Search, for instance, has been faced with the plague of spam blogs that are out to reap the rewards of online advertising, with re-published content that's been scraped from other online publications.