I have a jailbroken, iOS 6, iPad 2 and at some point, it started forgetting my Apple ID. For instance in both the App Store and iTunes apps, at the bottom, instead of saying email@example.com for the account, it ALWAYS says Sign In. I have tried everything from Resetting Settings to deleting iCloud account etc. Also, when it prompts for the login, it's always totally blank, eg it does not automatically fill in user name with firstname.lastname@example.org, both fields are blank. By the way, trying to use alternate Apple ID's doesn't solve the problem. It definitely something in the Apple ID, App Store etc mechanism on the iPad that's gotten corrupted or doesn't like something with Cydia etc.