So today, as a background task, I did a full rebuild of the site, so that the new MT scripts were properly referenced in the archive pages and so on. And lo and behold, it only took about an hour for comment spammers to show up again. Except this time it took only three or four clicks to select all the spam they had already posted, delete them, and ban their IP address. I'm glad I switched over to MT 3.1 or I'd be pulling my hair out again already.

Now to figure out how much bandwidth those invalid posts are costing and how to stop them if possible...