A trend I noticed on my sites lately: referrer spam is dying out, trackback spam is the main focus of spammers. This makes sense, since most sites only have one page showing their referrer statistics, if shown at all, while they usually accept trackback pings on every page.
For me it changes little, since the only page showing my statistics is not indexed by the search engines, and my trackback pings are perfectly protected by the combo MT-Blacklist and SpamLookup.
