Chasseurs d'Images (CDI) just published the first full technical test of the Nikon D200 - prototype. It was marked "Do not test" but they did it anyway and the results were so good that they decided to publish. They even did a direct comparison with the D70S, Canon 350D and Canon 5D.
It's difficult to resume 22 pages of test in a few lines. Basically it's all excellent. The camera is fully usable up to 1600ISO and even at 3200ISO the noise is still fairly low but the image sharpness drops off. Default image sharpening is moderate but the images still look excellent.
The only point on which any of the other cameras beats the D200 is on image quality. The 5D has less noise at high ISO, slightly more dynamic range, softer burn-out in the highlights beyond values 245/250 and a prettier out-of-focus image. (All this comes from the larger sensor).
Charles