When I upgraded the Drudge Retort, I wanted to simpify things by offering a single feed in RSS 2.0 format. Any halfway decent aggregator supports RSS 1.0, RSS 2.0, and Atom, so offering all three on a site just gives you two more things that can break.
I quickly discovered that the Retort has 212 subscribers to its Atom feed on Bloglines, none of whom were getting updates when I redirected the URL to the RSS feed. So I added Atom support to Wordzilla and recreated the feed.
Bloglines won't poll it, reporting an error. At first, I thought it was because I redirected the old URL to a new one that better supports caching. But no matter where I offer the feed, which is valid Atom 0.3, Bloglines refuses to check it.