I dont know, compared to peoples predictions it underperformed. But they only shipped 80K units so they were expecting to sell around that many initially (remember the Dec 09 stats are for 3 days of sales only).
Seems like it did fine. I think the 360 owners need to drop the mentallity for Japan that the PS3 owners have for the US. The 'next big game that will finally yadda yadda' mentallity. 360 haters (well , mainly rabid PS3 people) will just jump on this as an opportunity to take a stab at MS. (I guess they have been getting that kind of crap for most of their major releases the whole year).
PS360 ftw!
Currently playing..........
Gears of War 2, GTA IV Lost and Damned, Little Big Planet (Yes I said I had no interest but my girl wanted to try it and we did and now Im hooked 
)
