Dominik Wagner, developer of Carcassonne for iOS:

Game Center is supposed to be this fun and engaging infrastructure to enrich games and provide services like online matchmaking and connectivity. The idea is great, the infrastructure is really necessary, but the actual implementation is so bad almost all developers I know and talked about it dread using it. This has many reasons, some of them will be topic on this blog. But for now I just want to put attention to the one structural reason:

There is no internal client for Game Kit and Game Center at Apple

Anyone who's played Letterpress knows how broken Game Center is. Yet another failure in Apple's online services.

I've heard similar complaints from developers about sandboxing on the Mac. Since Apple often doesn't sandbox its own apps, myriad issues remain for third-party developers who are required to sandbox their Mac App Store apps.