This is an interesting topic. I have a D700 and a D7000 and am eagerly awaiting the D300s replacement. However, as I research the D800 further then perhaps it's may be worthwhile trading the D7000 for the D800 if test results reveal that using the DX crop on my 35mm lenses will provide sharp images when e.g. cropped to 100%+. The reason I say this is because a French interview on this forum has revealed that the noise the D800 provides equivalent IQ than the D700 at every ISO. Although a fps rate of the D700 and certainly the D7000 are desirable, maybe the slower fps rate of the D800 is not so much a show stopper if noise reduction is as good as the D700.
I would have to be convinced that the D800 Dx crops are as sharp as the D700 Fx images. That's going to take some time though.