I tried to figure out Movable Type’s Trackback a few months ago but I gave up because a) I didn’t quite understand it and b) I found the way it works to be a little intrusive. Tom Coates has come up with a pretty elegant solution by modifying the output of the CGI script and including it into the bottom of each post. I’ve done something similar using MT’s Standalone Trackback and PHP; if the post has no Trackback pings, then nothing gets printed, which is a pretty transparent solution I think. The Trackback URL can be seen in the article permalink.