As a further action due to the ongoing spam wave, I have disabled trackbacks and pingbacks on my site. I never really liked trackbacks anyway - the technical concept is ridiculous. Pingbacks are technically better implemented - due to the stronger focus on backlinking - but they are visually just awful: the technically generated excerpts just look like shit.
If someone wants to comment, they can comment - and a comment can also contain a backlink. And for everything else, there are the usual curiosity tools - and their link search works quite well (although I have also found mountains of link spam there - some stupid spammer pseudo-blog had a bunch of links to me for a while and ended up in my Technorati evaluations).
Since I am consistent, I will also no longer send out trackbacks and pingbacks if I don't accept them myself. Sorry, but my time is too precious to manually clean up garbage from a technically unfinished protocol ...