I forgot to explain trackback.
Here is the spec: http://www.movabletype.org/docs/mttrackback.html
And an example of trackback between weblogs: http://www.intertwingly.net/blog/1336.html
It is a method to notify a web site when you link to it. The linked to site can then present this information in its own way. My idea was to present trackback information as comments.
I made created a test implementation for lars-blogger, but I think there is a much greater potential to make is a standalone package to trackback enable any object.
See also:
The OSCOM conference has trackback enabled the pages describing the talks planned for the conference: http://lists.oscom.org/pipermail/participants/2003-April/000135.html
O'Reilly has trackback enabled the pages for their Emerging Technology Conference also http://conferences.oreillynet.com/pub/w/22/tutorials.html
