I'm not exactly sure all that it can do, but here's at least part of the story. (I'm posting this so I can get corrected if I don't understand the feature. It occurs to me that this post could use the feature, heh.)
Anyone, anywhere can send a message to any Movable Type server to associate a URL with a weblog post. That URL will be shown in the list of TrackBack links for the post.
Further, based on an email from Matt Mower, for some reason that I don't understand, this can only work with Movable Type servers. I doubt this, because from all outward appearances it is using HTTP, which could be emulated by any program capable of doing HTTP. Matt thinks this feature should be implemented with XML-RPC. I'm not sure it'll take off no matter what it's implemented in.
Here's the problem. By design it seems to assume that everyone plays fair. But eventually we all attract a relatively small number of people who would mark up every post with trash talk, if given the chance to. It's a predictable process. That's why I don't have a discussion group here (I used to), or a comments feature. It's why MSNBC is moving to weblogs over discussion software. It's basically why weblogs have a future for thoughtful discourse where mail-list-like collaboration tools are dead-ends. When I think about evolving weblogs, I try to avoid features that turn them into discussion groups.
» I think there has been a misunderstanding between Dave and I. Maybe I misphrased something or it was misinterpreted. Either way:
I'm not suggesting that TrackBack can only be implemented in MT. Just that, as it is implemented in MT it can only be served by MT and is most useful to MT users. It doesn't suit me very much. I also don't like the way you have to TrackBack enable things, use special URL's, have bookmarklets etc.. all that gets in the way to me.
I envisage an open XML-RPC based system. The TrackBack data should be available to & from any system and can track arbitrary URLs (no requirement to TrackBack enable anything).
Also with the prototype Radio client all the work of pinging is done for you automatically. As part of the publishing action Radio will figure out all the posts being referenced and ping them automatically. That's how I want it to work, you might want it different which is why I say it's a prototype.
As to the inherent design problem in trackback, well, I agree with the comments made. From a certain viewpoint.
However I see TrackBack not so much as a weblogging tool but as a k-logging tool. It gives you the ability to know what someone else is contributing to projects you are working on and that could be vital. As are discussion forums and all the other collaborative tools that help people do useful work.
Will TrackBack be absused? Sure. But so can any technology. If the abuse becomes a problem we can evolve strategies for addressing it. For me this is a time for experimentation, it's too early to abandon a potentially useful idea like TrackBack because it has a potential for abuse.
Example (and shooting from the hip) : Problem: "nusiance pings appearing on my TrackBack report." This seems a lot like the problem of spam email to me. Collaborative spam filtering looks set to deliver good results here, maybe it could do the same for TrackBack?
[Disclaimer: TrackBack - I am a believer!]