Types: comment spam, ping spam, spam blogs
Akismet: “87% of all comments are spam”
75% of update pings are spam (ebiquity 2005)
20% of indexed blogs by popular blog search engines is spam (Umbria 2006, ebiquity 2005)
“Spam blogs, sometimes referred to by the neologism splogs, are weblog sites which the author uses only for promoting affiliated websites”
“Spings, or ping spam, are pings that are sent from spam blogs”
Reading comments to Robert Scoble’s post questioning whether Microsoft really is the largest blog vendor I found this comment from Tim Finin of interest. Employing a machine learning model Tim and two of his associates at the University of Maryland conducted a study to characterise the Splogosphere. A PDF and powerpoint of the results are available here.