I recently went from a D70 to a S3 and I have to confess I was looking at D200 prices yesterday. The deal is that the S3 is worse in a lot of ways at the process of taking pictures than the D70, but the final product is far and away better than anything I've seen in other cameras. I got the S3 because of the sensor and that is still the best thing around. I'd love to try out the D200 for awhile and compare the image quality.
What do I mean by process being worse?
Auto focus isn't as good, it seems common to have it focus on the wrong thing. On the D70 you could select the focus point in the view finder. I haven't found how to do that in the S3.
RAW files are so large they become useless to shoot. A S3 RAW file is uncompressed and 25 MB. Couple that with a slow write speed to the CF card and you've got a problem. Actually shooting isn't that big of a deal for studio work. But if you want to play back you have to wait 5 or 10 seconds an image for them to be reloaded and displayed. This is a pain when you are showing what you shot to a client.
I hate sounding so negative because I really like the camera, and love the images. Put it in JPEG F1 mode and you get skin tones like no other. Here's one right out of the camera.