The difference WP-Cache2 has made my server load has been amazing. It was well worth the effort to get it installed (and to modify Alex's Popularity Contest plugin to make it compatible). But since I installed WP-Cache2, one of my friends has been complaining that my journal entries feed was returning with XML validation errors. I discovered that my feed was returning nothing a good percentage of the time. Someone in the comments section of the WP-Cache2 page had a similar experience, and suggested that disabling the feed cache fixed the problem. And so I did, and so it did.
There are two steps necessary to remove the caching of feeds. The first is to add your feed URL(s) to the "Rejected URIs" list in the WP-Cache2 options, and the second is to remove cache-related files from the "Accepted files" list.
Since making the change, I have manually loaded my feed a bunch of times -- it has worked, every time.
I also took the opportunity to fix the relative URL issue, and to change the feed MIME types. It seems that Wordpress 2.1.x uses text/html by default instead of the proper types. Although I use SVN to update my Wordpress installation nightly, my feed files are modified and are excluded from the updates.