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Agree with Ray there, although the focus confirmation dot is what I depend on most of the time and its very accurate, I haven't come across a situation where the results were off on the D800 (should be very similar to the D600).
Sometimes in low contrast situations, or low light (or adding teleconverters), the confirmation dot is hard to get, end up with flashing arrows instead. But the viewfinder for the D800, just like the D600 is very amenable to getting accurate focus also. Live view focus works best on a tripod.
Edit - yes, the focus confirmation dot works perfectly on AI, AIS, and even pre-AI lenses that a bunch of us have and are AI converted.
I have the D7000 and the D600 and the conformation is right on with both of my cameras. I have tested all of my MF glass with live view focusing and found in both cameras are very reliable. The D600's viewfinder is so good you will be able to see the focus with out relying on the focus conformation light.