I have just changed from a D700 to a D800 and first of all would agree with andy sharp, the D700 is a fabulous camera and one that I loved using. In particular, I thought its low light level performance for theatre work was outstanding. Even at ISO 3,200, it would produce slightly noisy but usable results.
Personally I found the transfer to be almost painless with very little trouble in programming the few changes into my old, personal memory banks! The major change that affected me was the AF settings and the transfer of the AF designation button to the front of the camera. It is all second nature to me now and I think it is simpler to use in many ways.
My main reason for changing was that I wanted to get at the new sensor because of its ability to auto focus properly with f4 lenses and teleconverters. It manages this significantly better than the D700. (there is a separate thread discussing this) The lower fire rate does not really worry me and the 36 megapixels is a nice bonus. You can boost the fire rate up to 6fps (I think) with an extra battery grip.
In studio, the better rear display is an unexpected improvement, especially in 'info' mode, and I have found it to be an excellent studio camera. The image quality is obviously very good, with the dynamic range being noticeably better- rather like the jump between the tonal subtlety of 120 film when compared to 35mm film. You can blow images up to a very impressive degree retaining a quality that is significantly better than the D700 and I think the White Balance is better, even 'Auto WB' that I never found was that good on the D700. The manual setting for studio flash is absolutely spot on, requiring no adjustment at all after shooting. The 'video' capability? Dunno, I have never used it! I probably will one day though.
Bad points? Not much really. The battery does not seem to last quite as long and it is a complex beast to use but then so is the D700. On the whole, I am glad that I changed but regret not having had enough money to have kept the D700 as well!
I also think there is quite a lot of misleading information about what lenses you should or should not be using on the D800, most of it rather shameless marketing hype. Your lenses are going to be just as sharp as ever, the only change being that the resolution of the sensor is now possibly able to outstrip the resolving power of the lens. Big deal! That happened with fine grained film for decades as well! I still use my old 28-105mm AF 3.5-4.5D lens that is really only a budget priced 'do it all, carry around lens' that produces very good images, just as it always has done. Even the 'macro' is pin-sharp and I have absolutely no intention of getting rid of it because someone tells me that I should use an 'approved' lens!
