All clear.

If by chance you use FeedBurner to distribute feeds and also the "MyBrand" service to use your own domain name CNAMEd to a Feedburner.com domain name, there's one catch to the migration to Google Accounts and hosting: your setup will be borked.

What you need to do is, after you've migrated, go into the mybrand control panel and delete each of your domains, hit "save", then add them back in.

This is obscurely documented in this post hidden behind a door marked "do not click upon fear of death by tiger": Older Known Issues & Workarounds.