Game Center Design

I've read numerous forum and blog posts recently and initial reactions to Game Center from Users is:

The login (UIAlertView) sucks and looks like the app is trying to steal my iTunes Account.

This is a good place for a pre-sign-on modal view or alert, asking if they want to use Game Center and explaining that the next dialog box is required to log into / authenticate with Game Center and is provided by Apple. If the user doesn't want Game Center then disable it and prompt them no more. Also let them know where to turn it (Game Center) back on should they want to use it in the future.

Just my $0.02 :-]