Matt has added TrackBack functionality
to Metafilter as an experiment. I've done the same here as an extension of my previous experiment
. Now, if you blog with Movable Type via a bookmarklet while on this page, you'll get a list of the posts that you can TrackBack. It's pretty cool.
It wouldn't be very tough to write a TrackBack Blogging extension for any tool that supports the Blogger API. That way people with other tools could participate. It's definitely easier when it's built directly into the tool, though.