i also ran into problems using live view on the d600. i contacted nikon and got some silly replies so started looking online and found this thread.
i enjoy taking night shots of large man made structure such as a factory on a river or a major bridge. typically i would put my camera on the trip and use live view to zoom in on the object to find a focus point and manually focus the camera. in many cases it is too dark to focus through the view finder. i find this to be the most accurate way to focus. i can leave the iso at 100 set the camera to f8 and use a 10 to 30 second shutter speed to get amazingly sharp images. this always worked on my d7000, d200 and d80.
this weekend i put my new d600 on a tripod and attempted to do the same thing. i was at iso 100 f8 and 20 seconds. i hit live view and i was presented with a basically black image with some noise running through it.
i took the picture and it was properly exposed. the confirmation image looked fine but the live view would not preview the image at the proper exposure. i had the brightness turned all the way up on the rear screen. the issue was that the preview was under exposed by about 9 stops. i was able to focus the camera by reviewing the image but that was a painful experience in trial and error.
everything else on the camera works great such as the menus or live view when ther eis enough light so i feel like it has to be a setting. the camera is too accurate even in low light for me to believe the live view is less effective than every other nikon dslr i have ever owned. i tested the issue on a nikon 50 1.4 af-d, 85 1.8 afs, 24 2.8 ais, and a nikon 70-210 ais as well as a tamron 24-70 2.8 vc.