To those who were affected by the recent problems in the RSS, you have my sincere apologies. It seems that the WP-SuperCache plugin doesn’t work nicely with PHP in safe mode (thanks to the How-To Geek for turning me on to the solution). Since MediaTemple switched it’s GS service over to PHP in safe mode recently, there wasn’t much of a precedent to go off of when debugging.
Anyway, the supercache has been disabled (just relying on wp-cache now) and the feed seems to have been stable for a while now. Once again, I apologize for force-feeding you invalid XML!