LiveJournal can handle RSS/Atom feeds pretty much the same way it handles any other user or community: if someone creates a syndicated account for a feed, users can "friend" it and comment on posts there. This is convenient for people who already use LJ and want easy access to a couple site feeds (I don't think it would be usable as a full-fledged newsreader, but I guess it depends on how many and what types of blogs).
As of this writing, 44 people read this blog via it's syndicated account (wave!). It's not a lot of people, but my readership is pretty low, so that probably accounts for most of my audience. Since the account acts like any other friend, these people see my posts smack in the middle of their friends page, and thus, can easily comment on posts there. Read more »