I'm bored of deleting comments by hand. So, I wrote a little antispam plugin. This plugin creates a token that expires after a given period of time. This token is used as a hidden item in the comment form. If this token is expired when the form is submitted, the comment is rejected.
Spam seems to come entirely from solo-connection POST requests. This means that the bots don't bother viewing the page first. In theory, the bots will be using a cached idea of the form, which will be expired. We'll see how well this works.
Right now it just uses a timestamp. If that fails, I'll add other tokens such as source IP, etc. Perhaps cookies too? This should be simple to filter out, becuase the spam bots don't act anything like humans with regards to browsing behavior.
I have enabled the plugin on this site. I'll post the source when I see it actually working correctly.
Waiting for spam bots to come by is boring :(