Sorry to hear someone so disappointed with their D800. I am absolutely delighted with mine (and could very easily afford to dump it if I weren't happy). Until I got the D800 I was a medium format film bigot but the D800 is so sharp I haven't used the M/F gear since. I shoot mostly hand-held and images are sharp almost beyond belief so almost wondering if there could be something wrong with your unit. Thom Hogan has pointed out the D800 is mercilessly revealing of lens flaws. You need the best glass in order to exploit the pixel density but given your years of experience doubt this is the problem. I am using the 24 - 70 mm, 105 mm Micro-Nikkor, the 300 mm F/2.8 and some primes (200 mm, 35 mm etc) which are premium len$e$.
Your comment about the camera being under-powered in respect to its computing electronics has some merit. The huge image files do take longer to transfer into the card and you can run short of processing capacity in burst mode (I do not notice any compromise in focusing accuracy, however). I would expect sports shooters to notice this. My photography is mostly landscape, nature/wildlife so don't need blinding speed where buffering is concerned. My priority is image quality above all and there the D800 delivers the goods in spades. I consider it something of a connoiseur's camera less suitable for the "speed means everything" crowd but for the careful worker hoping to extract the maximum from an image with the very best lenses.
I'm not doubting your experience at all and appreciate your candor. I have been using Nikon for small format photography since 1968 (How's that for one-upmanshi ) and the D800 is the very best so far, finally challenging my beloved medium format film for a lot of large image work. It is not, however, for everyone and probably less general purpose than some other models we have seen from Nikon.