Annoyingly I've been receiving a few comments lately that are clearly spam, most of them as anonymous. I've therefore taken the step of not allowing anonymous comments to see if this stops it. I'm really sorry if this is inconvenient for anyone genuine who wishes to comment who can't - it does still include open ID as well as google accounts, so I think most people would still be able to leave comments.
What a nuisance these spammers are.
And if any spammers are reading this, I do remove your comments, so it's not worth your efforts.