For some reason, my Feedburner feed was empty as was the WordPress-generated one. I was bouncing back and forth between the two, looking for clues, and was thinking it was a chicken-and-egg problem. With the Feedburner plugin, it redirects some of your feed files to your ‘authoritative’ Feedburner URL. The one for my blog is http://feeds.feedburner.com/BrianWhite. I wasn’t sure where the problem was, but suspected it was the WordPress side, as wp-atom.php, wp-rss2.php etc. were all blank.
I found a solution searching for [wordpress feed empty], the result being http://wordpress.org/support/topic/170629. Based on the info there, I added this code to wp-feed.php before do_feed();:
query_posts('showposts=10');
It’s a hack, but for now it works until the next update 
This bug tracking page was referenced in the aforementioned support topic, and the ‘milestone’ field says 2.5.2, so I expect that when I use the Subversion method for updating the blog, fixed versions will overwrite my hack.
It also appears that this happens on blogs like mine, where I publish at the root instead of in a /blog/ subdirectory.
Buss Crap. Doesn’t do a dam thing. Outdated crap.