Just had a quick look on one of the larger BT trackers. These are the total downloads for some recent games (i.e. not just the current number of seeders/ leechers)-
COD6 (PC)- 15562 (over 3 torrents, including 2854 who downloaded the crack for the Steam version)
COD6 (360)- 9187 (over 4 torrents, including 116 downloads of the German version)
Dragon Age (PC)- 11405 (1 torrent)
Dragon Age (360)- 3621 (1 torrent)
Batman: AA (PC)- 17901 (over 2 torrents)
Batman: AA (360)- 10667 (over 2 torrents)
GTA4 (PC)- 50901 (2 torrents)
GTA4 (360)- 25889 (2 torrents)
COD 4 (PC)- 63950 (1 torrent)
COD 4 (360)- 14470 (2 torrents)
In comparison, some other, heavily pirated PC games-
Crysis- 77535
Assassin's Creed- 157,869 (!)
Fallout 3- 30,897
Far Cry 2- 25,338 (~9200 on 360)
DemiGod- 8537
And some 360 exclusives-
Halo 3- 12701
Forza- 16029 (including both PAL and US versions)
GOW2- 14493
For the Wii-
Super Mario Galaxy- 12207
Mario Kart- 13302
None of the figures really means anything, but the impression given that PC piracy is massively, wildily in excess of the 360 isn't really borne out. Sure, it's 3-4 times higher, but then the potential PC market is probably 3-4 times bigger. For recent games, it actually seems like 360 piracy is catching up, although with up to 1 million XBox's being booted from Live this week, maybe it will take a back seat for a while.