I just thought I'd share with you my thoughts about upgrading from a D700 to a D800; or rather why I chose not to!
My main working body is the D700 and I love it. I used to have a D300s as back up, but when comparing image quality between the two; I was slightly dissapointed with the D300s. As a result, it hardly ever got used and so I sold it late last year.
I've then spent all winter considering weather to get a second D700 or upgrade to the D800. I've read lots of previews, of course there aren't many true reviews out there at the moment.
At the end of the day, I decided I loved the D700 so much that I would get a second. Here are the main reasons why (I'm not saying this as a matter of fact, it's just my opinion):
1) 23 Mp represents 3x the pixel count, however the proven low light level qualities of the D700 are because although 'only' 12 Mp, the pixel size is larger, meaning they work better in low light. 2) 23 Mp's will generate huge file sizes and create storing/backup issues. 3) I don't need a DSLR with video.
I see Nikon have released an online D800 users guide which seems to include some intereting caveats about using the camera and image quality issues?
Anyway, as I said before.... I've decided to stick with the D700 rather than simply be blown away by the pixel count. Hope you find this an interesting basis for a discussion?