Despite various anti-spam attempts, it appears that I will lose this battle unless I take advantage of Typekey in some way, so I had another idea. I've setup a Typekey account called 'noone' ('anonymous' was already taken, so my idea is probably far from unique). It's password is 'noone'. Clearly, some one could login and screw with the account info, but really, what's the point?

So I am updating my templates for a trial period in which I will require all comments to be registered or otherwise be moderated, but if you choose to remain anonymous, you are free to use the 'noone' account to do so. This will be the first entry that features this requirement, if you wish to test it out.