This site continues to get 10-30 comment spams a day, along with the occasional comment to an old post that makes it worthwhile to continue offering the opportunity for reader feedback. I'm thinking about switching to a comment form in which the only way to add bold, italics and links is to use buttons that add the formatting in a markup scheme that nobody else on the planet uses. Comments that use HTML or Markdown would be rejected.
Coming up with oddball and ultimately futile anti-spam techniques is a long tradition around here. In 2006 I invented comment flak, a system of putting fake form components on a page and hiding them with CSS so that their use caught spammers. It did not work.
Wait. Why didn't it work? How did the spambots figure their way around it?
And, um buy Viagra or something. ;)
Many of the newer blogs are using Disques commenting software. It works really well at cutting out all the spam. Not sure of the cost involved, but it's worth taking a look into.