Before going to bed, I thought I'd check the logs really quickly to see if anything looked amiss, and, sure enough, I'd screwed something up moving to the new software. I'd been testing the new software at a different URL and forgot to tweak one of the settings when I moved it up to the root. As a result, the links for all the RSS items was messed up, which caused automated aggregators to start trying to fetch from the wrong location. It should be fixed now, I hope this hasn't screwed anything up permanently.