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.