After talking to several other site owners, it seems the sudden increase in trackback spam that this site has undergone in the last week or so isn't an isolated event. I use Akismet
on this Wordpress setup, but 150 comments got through from the time I left work today until after dinner. Most of that was trackback spam. I had turned trackbacks off in the admin panel a while back, but discovered that there's no reasonable way to shut them off retroactively, leaving about 400 posts open to this crap. I had figured that I just needed to do a quick SQL query to shut it off on the old posts too, and finally looked tonight and ran this little query. We'll see if it at least stops the trackback problem.
UPDATE wp_posts SET ping_status = 'closed';
We seriously need a fully Bayesian filter for Wordpress. Now.