I have noticed that my D800 feels like it exposes about a third of a stop lower than my D700 did, especially in the shade.
I also feel like my shots are not very sharp. Since I live near the Nikon repair center in LA, I may take it in and have them take a look at what is going on with the focus. It's just subtle enough that I wonder if it's my imagination. I have tried to test it, but I still can't tell.
I It must be really nice to live near the repair place. I hate sending a camera in becaue it takes a while and they have failed to fix it under more than one occasion. (hot pixels came back unaltered. I have since learnd to live with them.)
Mine is extremely sharp but it is user dependent.
I shot images of downtown st. Louis directly across the river from the arch. Mi used a tripod with exposure delay.
Some of them were so sharp I could see the cables holding up the flag pole across the mississippi. It had to be at least 3/4 of a mile to that flag pole. Others shot under the same conditions would not show the flagpole supports.
Different is good!!! I just took few pictures of the lemon on my tree in bright sun. Before with Canon 5D2 and 7D there was always bright spot there. I could either underexpose or reduce exposure in RAW. The problem is that brightness of the spot was always different so different exposure compensation needed. Now exposure with D800 is right on the money. The reason you are getting slightly underexposed images because you have very bright spots in your picture so camera is trying not to blow it.