Hopefully this is the last that I have to say about trackbacks. They're done and tested. The code is up, the new scripts distributed, and they're working. The auto-detection and such appears to be working with MovableType in both directions, which is good.
I don't expect there to be much more about them — knock on wood — they don't have the same range of possibilities that comments do. Time will tell, of course, but for the time being I think that the current implementation is complete.