All right, it appears that my Atom feed fails to validate (thanks to Danil for pointing me to the Feed Validator). I'm not really sure how to fix it, but I have verified that the current version of MovableType does indeed have Atom support built in, so what I'm going to do is to upgrade to that version over the weekend and hope this does the trick. I'm guessing I'll have to remove my existing Atom.xml file first, but we'll see - I'll probably ask the question on the Support Forum before I proceed. In any event, I'll post an update when I believe my Atom feed is all better. Thanks for the feedback!