The symptom is iTunes experiences a timeout error when the user attempts to turn on the Genius feature on a Mac that is connected to the Internet via a router.
A possible fix is to connect the computer directly to the cable modem. Allow Genius to turn on, then re-connect the computer to the router. Once Genius is turned on, it should continue to update your music ratings successfully.
[crarko adds: Hard to say if this is a bug in iTunes or just something funky with the network setup.]

