Just from personal experience, I know piracy has been very bad since the original PlayStation days. On Ps2/Xbox it was just as bad if not worst.
On 360 it probably isnt that bad for 2 reasons: a) people think it will get them banned from XBL, and b) people dont want to void the warranty incase they get RROD
I remember someone posting download stats from God of War for PSP and it showed almost 1 million ppl got the game off torrent sites. That's a HUGE amount of piracy and certainly hurt the game sales.