WordPress 1.5.1 RSS bug
The RSS problem I mentioned the other day was not limited to just me. The WordPress 1.5.1 upgrade had a major RSS bug. If I understand correctly, the RSS feed was only generated for 24 hours after a new post was made. After that, it just returned a blank page.
Official bug fix:
Replace your wp-blog-header.php in your root WordPress directory with this one.
I ran across this fix here. Thanks for the pointer!