10 million units in the US, because the Wii will not only hit that number, but probably surpass it this month. Deutsche Bank analyst Jeetil Patel did the math and found that the Wii currently sits at about 9.5 million units in the US. If Nintendo's console sells another 700k units (like it has been) this month and the Xbox 360 sticks to its 200k level, the Wii will blow right past its competition's US install base.
It'll also be interesting to see the impact Wii Fit has on the numbers when it launches next week. Microsoft can take solace in knowing that it can always fall back on saying the Xbox 360 still has the "largest global install base of any current gen, high definition gaming console" ... right?