If you are the type of Android smartphone user that likes to apply different ROMs to your device frequently and use Google Play Music, changes been made you need to be aware of. Google is apparently now limiting accounts to 10 device deautorizatons. Once that limit is hit the user can no longer deauthorized devices, which means new devices can't be added.
Google hasn't officially said why it's doing this, but it seems almost as if they want to prevent people from flashing their devices frequently in accessing music. Some users who have hit this limit report that an e-mail to Google customer service has been successful in having older devices removed from the account.