A few days ago, I logged into my server and typed chmod 644 mt-tb.cgi. Yup, I turned off trackbacks. I found that even with a trackback Spam filter like MT-Blacklist, it was just getting to be too much. Dealing with it took time, I worried about missing some of the offensive crap, and, frankly, I just don't want to look at it. This is an example of a great idea dealt a series of, perhaps fatal, body blows by the lack of a credible identity infrastructure on the Web.
Now, before you leave a comment saying "did you try X?", understand that I'm willing to spend time setting something up, but I'm not willing to spend anymore of each day dealing with Spam. So, if requires substantial care and feeding, I'm not interested.