It looks like Microsoft started banning users from Xbox LIVE for playing Forza 3 and Borderlands early (the game was leaked on the internet a few days ago). It’s not the first time Microsoft puts out the BanHammer from playing leaked games and it will certainly not be the last time. For now it seems to be an Account BAN and not a Console BAN.
Here’s a quote of the email banned users got from MS:
Notification of Permanent Suspension: Pre-release title play
This email is to notify you that your Xbox LIVE account privileges have been permanently suspended due to illegitimate pre-release title play.
During your suspension, you will not be able to log into Xbox LIVE. Your Xbox LIVE privileges will not be reinstated.
Customer Support is not able to modify or provide any further details about your suspension.
Microsoft expects that all customers abide by the Code of Conduct. The Code of Conduct provides guidelines for appropriate behavior while using the service.