>So I picked up a used D90 recently to have as a >back-up and was comparing images, and it seems the 90 is >sharper in all of the ISO settings that I used. Can anyone >shed any light here? In my test I used all the same body >settings, same lense, tripod mounted, same distance, >everything the same.
The problem may be that you also used a relatively slow shutter speed. The greater pixel density of the D7000 sensor shows slight camera movements, shake, etc., as blur. The lower pixel density of the D90 is much more forgiving - unlike the D7000, the same slight camera movement doesn't always show up as visible blur in shots made with the D90.
The simple solution is to speed up your shutter whether you're shooting handheld or from a tripod. Do that and your D7000 technical image quality will suddenly start to look much better than the D90.
I have the feeling that many of us got used to unrealistically low shutter speeds and less than optimal handheld and tripod technique while using 6, 8, 10 and 12 megapixel cameras. We never could have gotten away with that back in the 35mm film days. But forgiving pixel densities and VR spoiled us to some extent. The new breed of higher resolution, high density sensors of 16mp or more demand better technique and faster shutter speeds.