Just a quick update to let you know that together with the release of iTunes 10.1.1 earlier today, Apple seems to have fixed the “missing Genius Mixes” reported by many users last week.
Either built in 10.1.1 or a server-side fix on Apple’s end that has been deployed today, go update your iTunes now, activate and / or update Genius (Store -> Turn On Genius, Store -> Update Genius) and enjoy your Genius Mixes again.
[Thanks, Jonas]