It's a great sale if you want the kit 24-85 lens, but from my experience it's pretty awful unless you really don't have anything else to use. f/3.5-4.5 and insane distortion at every focal length. It's sharp in the center but never at the edges.
This is a temporary sale, NR reports that it's only active until the 19th.
IMO despite the strengths of these new sensors, neither the 600 nor the 800 really hits the mark that I and many others are looking for. The 800 is too slow and its files are too unwieldy, and the 600 is too plasticky for my tastes. I would love it if they dropped the D600 sensor into the D700 body; I love my 700 and consider it the gold standard for semi-pro bodies even after the release of the D800.