University College of London published poster on Kinect depth accuracy evaluation:
"Performance Evaluation of the PrimeSense IR Projected Pattern Depth Sensor"
Jan Boehm (Supervisor)
This is the first systematic study of Primesense accuracy that I've seen in open sources. The depth resolution degrades with distance. It's 1.8mm at 0.5m, while at 3m it degrades to about 25mm. Note that Microsoft Kinect spec calls for 1.2m-3.5m range.
There is a circular hole observed in the PrimeSense point cloud where no depth data has been returned: