I was chatting to a photographer working for a private air ambulance company thats based with us at work a few weeks ago.
He shot with the D800, he said it was a fantastic camera but it had changed the way he shoots. The sharpness and level of grain in the pictures overall was greater than he had expected.
He now frames a shot with much more space at the sides to allow for crop. In short he said that only 1/2 to 2/3 of the sensor is usable for a pro photog making the camera a very expensive 16-24mp system.
The most interesting bit about speaking to him was watching his shoot. He used 12 bare flash guns to shoot the aircraft, positioning them both outside and inside to get the looks he wanted.