I fell for the hype and bought a new D800 along with some top Nikon lenses. The D800 does have amazing ISO, but it is very difficult to get the sharper images that it should be capable of. In the end, when I could not find a lens competitive to the 100-400mmL, or 24-105mmL, I resold it and just used my Canon equipment.
If it weren't for the situation at the time with no high quality affordable long lenses, poor liveview, and excessive time to process the large files on my PC, I'd still have it.