Microsoft's Kinect sensor passed the 4 million unit mark as of last week ending December 11th, according to VGChartz.
"This puts Kinect on pace to sell over 6 million units by the end of the year. Xbox360 hardware sales have seen a significant lift since the launch of Kinect with around 40% of all Kinect sensor sales worldwide coming via units bundled with Xbox360 hardware.
In the same timeframe from launch, Nintendo's Wii managed to sell 2.9 million units and Sony's PlayStation Move sold just over 900,000 units (camera + at least one Move controller) - less than 1/4 of the sales of Kinect."
A fairer analysis will be available after 3-4 months from launch (when the effect of seasonality and shortages will even out) and we will revisit these comparisons at that point.