Is there a process to determin if the Auto Focus is working properly. I have taken about 100 photos with my new d200 and if i zoom in over 65 the pictures are not focused well. How much should you be able to blow up a digital picture before the edges pixcilate?
50% is A3 on many monitors. Do you print bigger? Bear in mind the more you magnify the steadier you have to hold the camera to get a sharp result.
Next have you read Darrell's front page articles on the CAM 2000 (a lot of which applies to the D200) and measuring AF sensitivity areas. When the D200 focuses well is influenced by the AF targets selected - see page 59 of the instruction book.
Photography is a bit like archery. A technically better camera, lens or arrow may not hit the target as often as it could if the photographer or archer does not practice enough.