The first thing that impressed me over the d7000 is the accuracy and speed of the autofocus. In AF-C, my dog was WAY too fast for my D7000 autofocus as he couldnt keep up.
The D800 is a little more prone to camera shake then my D7000 tho, but that's something that I can live with. It works well in high ISO so a higher ISO setting to get a faster shutter speed handles a part of the problem.
The extra resolution gives more options when it comes to cropping a picture to make post shooting composition and like Diver said, it really shows up in the overall quality.
My only gripe for now is how noisy the mirror is when it comes up and back down. I will get used to it.
I really like the overall design and position of the controls compared to the D7000, having quick ISO access and metering options for autofocus is really a must. And the extra customizable buttons and the four settings banks are also a plus. On the D7000, the ISO button is at the back of the body, you get only one customizable button if you use back button focus and no settings bank.
Really like it so far. At a point where i'm wondering if i'll ever want to use my D7000 ever again. Time will tell.