I think iOS 5 is confusing Apple ID and MobileMe login. I tried to install a free app, and the Appstore on my iPhone popped up a dialog that told me to enter my Apple ID password. It specifically mentioned "Apple ID", not MobileMe login. But using my Apple ID password did not work. I tried again with my MobileMe login, and that worked.
So is Appstore now tied to my MobileMe login, not my Apple ID? Does Apple expect the Apple ID and MobileMe login to be the same?
When I signed up for MobileMe, I tried to get the same user name and password as my Apple ID, but it wouldn't have it. It forced me to make them different. Now they must be the same? When Apple asks for my Apple ID, it really means my MobileMe login?