I don’t know what it is about Trackback that makes it utterly impossible for anyone to explain it well. Certainly the How Trackback Works (from cruftbox.com is a scruffy but noble attempt to make it comprehensible to people. But I think it’s going to fail because it explains the process before it adequately explains the concept. I think it has another failing too: it concentrates on explaining the mechanical and clunky ‘do it by hand’ approach of getting trackback URLs and pumping them through the ‘pings’ interface. No-one’s going to get it until everyone’s using autodiscovery.
Ben and Mena Trott’s version (Trackback for Beginners) is well-written and comprehensive, but essentially incomprehensible. I think it’s because it doesn’t concentrate on explaining the core uses of the functionality (get person x to automatically link back to me when I post something about them), but instead tries to go right back to first principles. Personally I’m not only not interested in someone Trackbacking my site simply in order to get a mention, I’m actively against it and don’t think they should be mentioning it – let alone promoting it. On a weblog (at least) there’s got to be reciprocity of some kind otherwise it’s going to be the most-spammed feature in online history.