The Nikon D800 adopts many new features from the D4 (The D800′s big brother to say), such as the same Advanced Scene Recognition System with 91k-pixel 3D Color Matrix Metering III, 1080/30p HD video with 20 adjustable audio levels and uncompressed HDMI output, in-camera two-consecutive-shot HDR and Active D-Lighting. In addition there is a difference in resolution (remember, more megapixels doesn’t translate to better quality images), you gain a 2.7x in focal length (effectively multiplies the focal length of any lens by 2.7) which means it will bring you closer to your subject without the need to a longer lens or teleconverter (very handy for those on a budget).
The Nikon D800 isn’t the most compact full-frame DSLR that Nikon’s released to date. It’s noticeably taller than the D700 (by roughly half an inch), with a higher pentaprism and smooth appearance. But a new body design isn’t the only element differentiating the D800 from its predecessor. The camera offers excellent contrast-detection autofocus, allowing you to sharpen your subjects much more quickly while in live view.
The D800 also offers video improvements, and lets you capture 29 minutes and 59 seconds in a single clip in normal quality mode because of the D8000′s larger footprint, you’ll need to upgrade your grip along with the camera. The MB-D12 attachment uses the same battery as the D4, and boosts the camera’s burst mode from four frames per second to six in DX mode.
And what about price? As to date Nikon UK hasn’t given a date (To my knowledge) but as seen as I have one Ill do a update : D
As for launch dates the end of April is a rumor.