…you should have a look at this post at engadget:
Okay Nikon owners, stop laughing at your 5D Mark III cronies for their leaky problem. That might be a drip in the pail next to your own worries — namely, possible “lock-up”, focus and viewfinder hitches on your D800 or D4. Nikon verified that a “small number” of units of both DSLRs can lock up and become unresponsive, but until there’s a permanent patch you can prevent this by disabling both highlight and RGB histogram displays. The company also verified that a “run” of D800s is suffering from a viewfinder bug, although it has yet to confirm another emerging problem with autofocus in some units, which apparently requires a factory fix. So, if you’ve noticed any of this with your pricey new D800, or really pricey D4, your best bet might be to reach out to your Nikon repair center post-haste. And don’t let the Canon guys see you.