Before the D800 hits the stores and are really available could take a few months to say the least. Then, I'm not sure how many will absolutely want to get the 800. Not me for sure. I don't see the point (I'm just speaking for me now) to have these huge files to work with. I'm more than happy with the 700 as it is and, if I read what is said in other D700 forums, most users are so happy with theirs that they are in absolutely no hurry to change, specially with the $ involved in an upgrade.
Again, it's just my opinion and I'm certain it does not reflect all opinions.