No one has ever or will ever be banned for buying and playing a legitimate copy of a game before it's officially released. It is not the responsibility of the customer to adhere to street dates, etc and so, there are no legal grounds for any consumer to
be punished for it.
If people have told you that it's happened to them or if you've heard rumors of it happening, it's either completely untrue or there's more to the story that isn't being mentioned - something has to be rotten in Denmark for a banning to take place.
Enjoy your game care free and with the knowledge that you were able to get it earlier than many others. :)