I'm a Medium Format film bigot but the D800 has made a digital believer out of me. It is good enough that for at least half the photo projects I would have thought only MF could do the job I now take the D800 instead. I have made stunning prints at around 30 inches on the long side. You need the best lenses to exploit all those pixels at that density. The 300 mm F/2.8 Nikkor is superb. Also the 24 - 70 mmm and the 105 mm Micro Nikkor. Somewhat surprising, the bargain priced 70 - 300 mm VR does a more than respectable job from 70 - 250 mm. I would not consider a lens like the newish 28 - 300 although it is FX.
Simply a superb camera. Has far exceeded expectations mainly because of pixel density in a sensor that size.