Need to dig into this a bit more:
bq.. A thing about weblog trackbacks that bothers me is that you can do the same thing using nothing but link structure.
Trackbacks are used to notify the author of a web page A when another web page B has commented on it. The idea is to make the “commented on” relationship explicit. This is done by having the A page point to a form which the author of B can fill out. The net effect is like tapping somebody on the shoulder.
The ability to tap somebody on the shoulder is a good feature, but why this implementation? Users hate up-front work in a deep and enduring way. They will not do it if there’s an alternative, and in this case there are two: referrer logs, which take a tiny bit of work for the linkee, and Technorati, which takes no work at all.
In either case the secret sauce is the link structure of hypertext networks. HTML already provides a tool for correlating the source and object of a comment — links — so trackback is a solution in search of a problem.