I'm about to drop HubLog's RSS 1.0, RSS 2.0 and Atom 0.3 feeds, as it's too much trouble to maintain and keep rebuilding them (each entry has an individual RDF output - which is enough - and RSS 2 has little value any more).
Is it bad form to redirect them all to the Atom 1.0 feed? The alternative is to replace each of the feeds with a message saying there will be no new posts and linking to the Atom feed from there, requiring manual resubscription to the new address.
The third option, which seems best, is to redirect the old feeds to a Feedburner version of the Atom 1.0 feed. That way Feedburner's SmartFeed trick can give the reader whatever content it can handle. Tools that are expecting RDF will still get confused, but they should either be able to handle Atom/RSS or fail gracefully anyway.
Later... I went with the FeedBurner option, with a temporary redirect for now which will change to a permanent redirect if everything works ok. Here's the primary Atom 1.0 feed and here's the FeedBurner version. Hopefully everyone will get redirected automatically.