Christian Handl has done a very interesting comparision between Nikon D3 and Canon 5D at lower ISO settings and in the studio with some interesting comments on dynamic range and the ability to boost shadows without noise:

“The propagated fantastic high ISO-performance is actually very good, but for a Canon photographer less of a sensation, with a maximum of 1 Aperture advantage over the Canon 5 D, I would say after the first comparisons. But in other words, for a Nikon photographer an improvement of 3-4 steps to the D2X, which is a very impressive difference.”

and

“Most surprised me the far greater dynamic range, here are the differences in my recordings to the Canon 5D very large, the cameras were in similar light (same flash unit and similar ISO from 250 to 320) to allow a good comparison. While the black clothes of the model in the 5D were only partly illuminable, with the D3 even the seemingly blackest parts of the dress showed structure without disturbing noise. Very impressive, and in everyday life in many photographic situations more important than MP“