UPDATE: I posted about this on DPReview, got some helpful responses suggesting that there are issues with my shooting method. That DPReview thread is here if you want to check it out. I have done follow up experiments that are inconclusive as to the advice given in that thread. The D600 still appears to overexpose. I will do a followup post about it.
UPDATE 2: 2nd set of experiments here
I've shot with a number of cameras and they all tend to have different exposure tendencies. For example the Pentax K100D and Fuji S5 attempt to avoid blowing highlights, often producing straight-out-of-the-camera (SOOC) images that appear underexposed. The Nikon D80 doesn't seem to be very concerned with highlights and produces SOOC images where the subject is correctly exposed but the image often has blown highlights such as in the background. Then there are cameras such as the Nikon D70 and Nikon D3 which in my opinion have a balanced exposure (taking into account the limits of the sensor's dynamic range).
In this post, I took some test shots with the D600 to evaluate whether the D600 has a tendency to overexpose or underexpose. All shots were taken in raw and processed in View NX2.