Got an e-mail from the good people at Hosting Matters over the weekend that comment spam activities on my blog were causing some significant server hits, with suggestions on what to do about it.
I already run AutoBan, a fine MT plug-in that, as soon a someone files a comment identified as "junk" throws up a temporary IP blog for the page, preventing them from trying again (with trivial load on the servers in so doing, unlike most of the other anti-spam solutions). Granted, IP addresses can be spoofed, but it's at least some help against some comment spammers.
There was also a suggestion to fix the way comments.cgi is invoked by TypeKey-enabled blogs (like this one). I've also now implemented that, which should help all-around.