I agree with Perrone - I see no advantage of using the DX crop over cropping in post processing, and would just get a DX camera if I wanted a crop most of the time.
The big disadvantage is the viewfinder is still FX, so the DX crop is composed using a smaller part of the viewfinder. It's not the same as viewing through a DX camera viewfinder where the viewfinder matches the image.
Given that a DX crop is smaller than a D300s image - and much smaller than a D7000 or D5200 image, you're just giving up too much.
Now the big positive of FX is since you are using a longer lens, you get much better subject isolation and a nicer background than the same scene with DX. If you have enough reach, I find FX to be more pleasing.