Just preordered the D7100 at my local store and was able to be #1 on the list. I have the D7000 that has been for me but feel that 24 mega pixels will help my type of photography. Not planning to sell my D7000 as I feel it will be a great backup body. I think for us getting older, the weight will help when traveling abroad coupled with my 18-300mm. I think next time I'll leave my D800 at home as my back can't support the weight any longer. Anxiously waiting for the release tentatively on the March 21.
Good luck with the D7100. I think it's a great next step for the D7000 line.
Regarding the D800 weight, you might consider using a shoulder strap rather than a neck strap. I bought a Black Rapid and don't leave home without it (when I'm photographing). I was considering a D800 as my next move, but bought a D600 instead due to the weight issue. For me, I sometimes have to shoot one-handed with the flash in the other hand and the lighter D600 is perfect.
"Red is gray and yellow white, but we decide which is right ....and which is an illusion"
I definitely second the Black Rapid strap (or similar). I have the Sport version from Black Rapid, and it's a night and day difference in comfort walking around all day.
I live about 10 miles from Circuit of the Americas in Austin, so I find myself able to go there a good bit. The BR Sport strap makes carrying my camera and a rather heavy lens quite easy and I don't even notice the weight.