I'm fed up to the back teeth with comment spammers, so I decided to do something about it. I do use the wpblacklist plugin, and that's a great help, but you still miss one or two items when a new spammer appears and you haven't updated your list. The majority of spam comments are made on old entries, so I decided to set up automatic closing of comments, as described here. I've set it to close comments after 14 days — that seems about right to me, but if anyone wants me to extend it a bit, just let me know. I've put a line in my cron file to run the script every day like this:
GET http://pathtoscript/auto-close.php > /dev/null 2<&1
It goes without saying that anybody (except spammers!) who wants to make a comment on a closed entry only has to email me, and I'll put the comment in myself.