I’ve gotten lots of comments on my posts on Blam (blog spam/comment spam). After reading all of them, it seems the most successful approach is the image that you have to retype to be able to comment. We’ve all seen these. They use them at ticketing sites, domain registration sites, etc to get around the bot problem. It seems that this works real well to stop comment spam too.
I’ve sent an email to TypePad suggesting they add that tool. I’ll let you know what I hear back.