I've been have somewhat of the same issue since I updated with the GM version and now I have the same issue in the public release.
-I go to use my email and it says the ID has never been used, go thru the setup process, and once I get to the last page where you enter a nickname it doesnt go any further so I presume Apple has built a newer Game Center for all the nifty things they said you'd be able to do in iOS 5.
---Sucks