>I few months ago I took some portrait shots of a family and >one person in the group would be tack sharp and the other >members of the family would be slightly out of focus. Of >course for these shots I had lights set up and of course a >tripod.
This sounds more like a DOF issue and not a problem with the sensor. Assuming the subjects were not in the same plane, did you stop the aperture down to f/8 or f/11? Good Luck and Enjoy your Nikons!