FOV for DX and FX lenses
... FX lenses work fine on DX cameras. DX lenses must be shot in "crop" mode on an FX camera to avoid vignetting. Crop mode only uses a DX sized part of an FX sensor so a 12 mp D700 ends up being 5 mp. Not a good trade-off.
(OP: "I just received my D800 ... ")
The D800 has
15MP on DX
... even the AFS 17-55mm f/2.8 works fine on FX from 28mm to 55mm, given that the circle increases with the focal. It isn't the same on zooms where the circle remains short at any focal (18-???) ... And do not forget, he can also use the 1.2x crop, where the D800 has
and the 17-55mm is a fine 20~55mm ... if someone is low budget and can not update his lenses, he can manage with DX lenses and update slowly.