After using the D800 for a few months it is obvious that the camera is capable of producing high resolution images if it is used correctly. The best advice I have seen is to treat it like a large format camera. That means using a tripod, remote shutter release and mirror up mode. In MU mode the first press of the shutter locks the mirror in the up position and the second activates the shutter and release the mirror. There is no point in pressing the shutter twice in rapid succession as the camera needs time to settle down after the mirror is moved. So, press once, wait a few seconds and then press again.
The most important things with the D800 is to use the best possible lens. There is no point in spending a heap of money on the camera and then sticking inferior glass on the front. If you cannot afford the body and a decent lens then economise on the body and maybe look at the D600 or some of the high end DX models. You will NOT get the best out of the camera with a cheap lens on the front.
The alternative to paying a lot for an F2.8 zoom or two is to use Nikon D prime lenses. They are much cheaper, easily available second hand and are sharp. See Ken Rockwell’s site if you need convincing.
Would I change the D800? For landscapes and portraits then yes, I would prefer a 5×4 with 2-3 lenses, 10-15 dark slides and large hefty tripod and somebody to carry it all for me, plus enough money to pay for colour neg film and processing which runs at around £8 a shot these days. And of course a nice black and white darkroom with a De Vere enlarger and cathomag head. That will materialise when a big lottery win comes my way.