I would love to see North America only numbers as well.
Not a lot:
As of January 22, 2008, World of Warcraft has more than 10 million subscribers worldwide, with more than 2 million subscribers in Europe, more than 2.5 million in North America, and about 5.5 million in Asia
Its had no new content since december, everyones done it to death. MOP will probably bring everyone back, plus a load of new players, (Ooooooh pokemon fights and farmville). I reckon It'll probably explode back to 12M+ subs again, dipiing again after christmas as the next content patch slips back.
I can't see it going back to 12 million subscribers again.
Blizzard has been stuck under that number since the Wrath of the Lich King days. Cataclysm wasn't able to get them back to 12 million, neither will MoP. 5 new levels? Why not 10 new levels like TBC and WOTLK?
Numbers dropping off before expansions actually is something new if you go by the graph. The game kept growing all the way up to Cataclysm launch, then numbers started to drop after. However, it does seem to appear that growth really slowed down in Q2-2008 compared to before, finally topping off in Q4-2010 and the game has been bleeding players ever since.