I've used it for one short film and I was quite impressed. A bit of moire, but much more less then the B camera which was a Canon 600D/T3i. As soon as possible I'm getting a NINJA2 a try that out. The downside of the whole Nikon DSLR is that your are focusing the other way that you are used to. Also, there isn't a way to connect a PL glass to a Nikon DSLR.
"You never want to get to get a call from the editing room"
We do a lot of video shoot work up in Africa and use the D800 as a nice light kit. Personally I think the Nikon D800 has more dynamic range than the Canon 5 mk3. It does have more moire though but it does allow you to record out to the Atomos Ninja. For moire we are busy investigating the Mosaic Engineering filter.
having used Nikon stuff over the last years I really liked the advent of the D800!
We now have shot a couple of different projects with the D800 and even at 38deg celsius right in the sun the camera worked well - no heat issues at all.
Picture quality is beautiful - I wish the output would send the 'picture profiled' signal.