Fuji and Nikon use the same bodies but their insides are different including the sensors.
The S2 Pro was the same as the D100 (almost) and the D300 is the same chassis and body as the S5. I liked the S2 over the D100, but I am looking at a D200 for the not too distant future but I have the added expenditure that I need a second body for wedding work and I may as well have that body the same as my first camera so an upgrade would be 2 x D200 and an Aquatica Housing. Best part of 2 grand for the whole sheebang
Scooter or new housing...