>> The feed is now working. Thank you for your patience!~
I think it has something to do with the Feedburner Feedsmith Plugin (version 2.3) and the upgrade from wordpress 2.2.2 to wordpress 2.3.1
Thanks to the reader who has brought this to my attention!
Unfortunately, after fiddling for a few hours now .. I have STILL not figured out what the heck is the problem, and opened up a discussion over at the Feedburner Forums.