There is a very interesting article in the International Herald Tribune that suggests that Rebrandt may have been well, a little bit wall-eyed, and that is not being about to see things in true stereo vision is part of the reason he was able to paint scenes from real life to the canvas so well. It also mentioned that this would of made him more attuned to shadows and light.
Being that I was born fairly crossed eyed, and after a surgery when I was three, now slightly (especially when I am tired) crossed eyed I found this fasinating. I've been told that I see 80% of the world out of my right eye and 20% from my left. And that because my vision has been that way since birth that my brain just wired itself to get depth preception. I imagine it was the same way for Rembrandt.