I noticed an interesting trend today: this blog has had 6 legitimate trackbacks and 36 spam ones. It's also had 200 real comments and 0 spam comments. The blog software has caught every single spam trackback and marked them correctly as spam. There haven't been any spam comments caught because I have not had a single spam comment since I moved this blog to Quick Blog.
You read that right: not a one. I think the CAPTCHA is the main reason. (By way of contrast, my WordPress blog gets about a dozen or two spam comments a day. It captures them all, but only because I've set it up so that any comment with a link goes to moderation. That's pretty tight and that's marking them for future review—an annoying chore.