comments.xml is now an RSS feed with just comments. The nice thing about this feed is each new comment is a new entry in it.
comments.xml is clean, according to the RSS Validator. The other feeds aren't and fulltext.xml in particular has some issues with it. But honestly, I'm tired and I don't have any more time today to futz with it. Besides, it's working in BottomFeeder, and as far as I know in any aggregator. (It wasn't clean before I started in on it - and I hadn't heard any complaints.)
Anyway, I've learned a lot about XML, RSS, and Movable Type in the last couple of hours, and I'll try to publish some of it later this week. :-) For now, please enjoy the shiny new comments feed.
If you're not sure you have the right feed for you, please select from the pleasing menu on the right or bottom of the entry.