With the release of iOS 4.1, Apple added a range of new features, one of those features was aimed at gamers and was called Game Center. Game Center lets you play games online with your friends.
It seems that the friends list on Game Center is capped at 500 people, so don’t go adding everyone online or your will soon run out of space on your friends list.
Once the 500 friends limit is reached the only way to add new friends is to remove someone from you list. To be honest 500 friends is quite a lot and most users will never reach this.
It was discovered by MuscleNerd from the iPhone Dev Team who had published his Game Center ID and was letting anyone add him as a friend.
via App Advice