I had mentioned the idea of using a script to close comments automatically in July last year and then thought about it when I started getting hit with comment spam later in October.

Now, a couple of weeks ago Jeremy posted the script he has been using for quite a while to do exactly that. Thanks! He uses mysql and I use Berkeley DB, so the script might need changing (honestly, I have no idea :)). Hopefully at some point within the next few days I'll have some time to look at it and start using it.