A japanese site features an interview with someone from the Nikon D300 development team (automatic translation to English by Google found here). Some interesting statements:

“a) they expect the high ISO noise performance to be more than 1 stop better than D200

b) they admit that the sensor is supplied by Sony. Although they say that the spec and the QC is done to Nikon’s standard.

c) they recognise that there is a market need for a lens similar to Ai Nikkor 45mm F2.8P, or other fast primes (to be upgraded).

d) The most difficult thing about providing a 100% view finder in a camera is the skill required in calibrating the viewer. Previously, it was only possible to manufacture units required for 100% view finder in their Japanese factory.”