Having become annoyed with comment-spam, I have chosen to implement Gudlyf's AuthImage plugin for WordPress. The plugin makes one of those pictures with funny text that's hard for computers to parse. The plugin also demands that you type in the contents of the image or you don't get to post a comment. I don't really like forcing something like this on people but the spam was pissing me off and this seems less obtrusive than sending peoples' comments to moderation and then accepting them later. If this is really unpleasant for people, let me know and I'll consider other options.