Trackback Threading
Greg Reinacker: So, everyone, how about implementing TrackBack and/or Pingback on your weblogs - and let's see where it takes us? My guess is that the next logical step is trackback threading. This represents a small challenge for those of us who comingle trackbacks and direct comments, but I'm sure that this can be overcome.
Amusingly, trackback is to linkbackparser as Mark's cite logic is to mine.