iOS 4.1 beta comes with a newly re-designed Game Center preview. Game Center in its original form was present in all the iOS 4 betas but was removed from the general, public release. Previously all dark and blue and ovaly, that remains in the sign-up sections but the new Game Center has a background of billiard-table green and fonts -- well, that make Notes' Marker Felt seem restrained.
The tabs have been newly re-arranged. Me features your name in huge, outlined ALL CAPS with friends, games, and achievements in elongated sans-serif backed by multi-colored ribbons. Status comes below that in serif, as does your account email address in both serif and ribbon background. (For those keeping count, that's 4 fonts on one page when you include the standard UI Helvetica -- quite a departure for Apple).
The Friends and Requests tabs haven't changed much though the new colors and fonts make them harder to read -- hopefully that's part of the beta that's still evolving. Games is currently empty except for a ribbon that teases "Find Game Center Games".
Apple's clearly still iterating on Game Center, and though some screens have leaked out, it remains under NDA so lets just hope they're using their time behind the scenes to really nail this whole "XBox Live! for iOS" concept.