I know that the D800 is not really the replacement model over the D700. Nevertheless, it did replace my old D700 and the D800 is, I believe, better suited for my photographic needs than the D700, i.e., studio, portraits, and landscape.

The D700 was and still is an outstanding DSLR. The D800 is of course better, but in a very perceptible way, which was quite a surprise to me.
I have done over 5000 shots since my purchase on 24 March. So far, no issues to report: no green cast from the LCD and no problems with the CLS system.
Nikon has really outperformed with this new DSLR and the clear improvements are:
- Much improved Dynamic Range, which was my main problem since my first DSLR
- Better colors straight off the camera: deeper and richer
- Better AF in low light
- Highly detailed photographs at full res, 100% magnification and also when down-scaling the photos.
Let's not forget a proper and useable HD video feature at broadcasting... Read more

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See that my purchase is verified by Amazon. Below are my observations after one month of ownership.

Pros:
+ Resolution: With the right lenses and on the right settings the detail astonishing.
+ Dynamic Range: Incredible, when shooting in lower ISO's it is near impossible to ruin a photo. Do an internet search for: "fred miranda d800 review Yosemite" to see real life comparisons.
+ Color: Adobe profiles in LR and ACR are horrible, create custom profiles using a QPCard 203 (Avail directly from manufacture) or use a MacBeth chart with Adobe DNG profiler for great colors.
+ AutoWB: Excellent, much better than the D3/D700. *** See Tip Below ***
+ Low ISO: Having a true 100 ISO is godsend for on-location studio lighting setups.
+ High ISO: The D800 and LR4 do an excellent job in controlling noise. Using PS plugins a properly exposed image can print acceptable 6x9's at 12800 ISO (max for D3/D700's is 6400).
+ LiveView: The... Read more

I'm a Sony shooter with only a few lenses. I use to shoot Canon during the film days. I tested both the Canon 5D mkIII and the Nikon D800 and here are my results. I tested a 5DmkIII with a 24-70 f2.8 lens and a Nikon D800 (not D800e) with a 24-70 f2.8 lens.

High ISO:
About the same, except D800 has a lot more detail to work with. In Lightroom, I can save a higher percentage of ISO 6400 shots because the D800 has more detail. Canon seems cleaner initially in Lightroom but when the picture fits into a 24" 1920x1080 monitor or a 64" Samsung plasma TV, the Nikon looks a tad cleaner, noise less noticeable. I think the Canon looks cleaner in Lightroom because it is just a smaller picture. But displaying ISO 6400 shots on a monitor or TV, Nikon looks nicer in general. Both cameras at ISO 12,800 look awful and not recoverable in Lightroom. It might look acceptable as a really small pic but why the heck would you buy an expensive camera to display crappy looking pictures... Read more