Microsoft - XBOX360, PC Games, etc.
Aye, the console gets blocked off XBL (so you could still use it offline), but the only way they notice if you've played a copied game is if you've downloaded a crap rip of the game and the CD tag is inaccurate (which is very rare). Even then if you do get caught you'll be paying £200 for a new console, which will be nothing compared to the amount of games you'd have had for 'free'.
I'm tempted to do it, only because you get games a week early, but haven't done it yet.
EDIT:
The only game I've known to have caught people out was a cracked version of Crackdown, and that was only people tried to use it to get into the Halo3 Beta.