Looks like Apple has just reset Game Center, their new social gaming network, and any developers testing the service on the Gold Master (GM) seed are now greeted with a "create new account" screen. Moreover, all existing Friends are gone, meaning if you intend to keep connected when iOS 4.1 goes live this week, you'll have to send and approve your friend requests all over again.
That is, if Apple doesn't reset it again before launch. But that's what development builds are for, right?
UPDATE: Apple has also confirmed compatibility for Game Center:
Yup, no iPhone 3G listed.