TBH, it will depend on what you shoot, and how you shoot. If you are shooting on a cloudy day outdoors in daytime, you will probably not see much improvement in IQ. But if you shoot in high contrast setting, you should see more of a clear difference in IQ. Dynamic range is wider by more than 2 stops, so shadow details are kept nicely, and relatively noise free. I think AWB is better in D800, too, although I mostly use custom WB, so not the best judge of that.
Regarding sharpness, camera bodies don't determine that as much as lens and focusing technique. If you want sharper image, make sure you got those covered. If you already have quality lens, you may need to fine tune AF, maybe?
I've had my D800 for less than 1 month, and I am definitely finding it superior to D3 in terms of pure image quality - I am keeping D3 for speed and robustness for weddings. But to be honest, if you don't see a difference in IQ, I'd go back to D700 and save the disc space; it's still a wonderful body.
