This is the first Nikon body I have bought. I am coming from Canon: 1Ds Mark III and 1D Mark IV. Canon's highest resolution now is 22Mpixel. I wanted more...
I miss the quality of Canon's L series primes, especially the 50/1.2L (the Nikkor 50/1.4G has too many aberrations) and the 135/2L (I don't like the Nikkor 135/2D because of the DC). But I am pleasantly surprised by the image quality I am getting from the 24-70 and 70-200 VRII.
It takes a bit of getting used to the differences between the Canon and Nikon user interfaces - turning the lens the opposite direction to mount and dismount it is probably the most irritating. I do like the direct access buttons on the left; direct access to ISO, etc, is convenient. Menus are a little less convenient.
The image files are large, as you'd have to expect, but the lossless compression (new? I thought Nikon only supported lossy RAW compression in the past) works fine. I was pleased that I could stay with CS5 (no desire to move to CS6).
I've been accustomed to using pro bodies with integral grips for a while now, and so I bought the add-on grip for the D800E. I'm not impressed - it's expensive, but it feels cheap. The joystick is horrid. For the price, I'd expect better quality controls. Also, the Canon grips (last time I used them, which was on the original 5D) hold two batteries, not one - there's enough space that they could have allowed for a second battery, but they didn't.