I've got a solution on the blog that seems to be dealing with spam - I just discovered some attempted comment spam sitting in an archive folder - exactly where I expected to find it. I haven't had a serious issue with spam on this server anyway; I'm not running one of the well known blog systems like MT, so I don't attract as many attempts. Having a homebrew system seems to deter a lot all by itself, but the extra checks I've got in place seem to be catching the rest (so far).