A few days ago I added support for tracking Wordpress.com comments, but its implementation leaves a lot to be desired, as I'm merely using comment feeds for the purpose.
The first problem is that Wordpress.com limits the number of comments in feeds to 10. Thus, it is very likely that comments will not be caught if the post has a large number of comments to begin with, or if more than ten comments are posted before the feed is checked again. This is an acceptable risk at the moment because I, as the sole developer, do not have many friends whose posts receive large numbers of comments.
The second problem is that comment feeds do not contain all of the information that I would like to have: author avatars cannot be determined from the information in the feed. Thus, Wordpress.com comments have no visual cues as to authorship (which is, of course, indeterminable anyway). This is a far more irritating problem, but I have to accept it for the time being.
Happily, implementing support for Wordpress.com has brought me closer to a fallback comment tracking method. The software should eventually be able to present the user with a list of all of the feeds that it has found, allow the user to choose which feed is the comment feed, and then track that feed.
I think I'm going to take some time off from writing support for more backends -- although I make it sound like this software is coming along nicely, it currently has no support for automatically updating tracked conversation, viewing comments is painful, and so on and so forth. The software doesn't even have a name yet! Plus, Django 1.0 is coming out in early September, and will introduce a lot of incompatibilities with anything I write now. So, I think I'm going to take some time, install Trac with Bzr support, and start getting more organized before continuing.