James Tauber has written up an approach to blog conversations, which he intends to implement in Leonardo. He referenced Danny Ayers' interesting post about blog entries as web annotation.

I had already considered POSTing to the blog entry as the mechanism for comments and that is when it first struck me that comments and trackbacks are really the same thing. The fields that you POST would be slightly different, but the mechanism should be the same. Source.

(Technorati Ref, Topic Exchange Ref)