Well I got mine a few days ago. I'm really liking it so far.
One of the first shots out of my new D600. This was from an in camera JPEG. I've added some falloff, did a curve adjustment, and did the BW conversion in Photoshop.
ISO2000 on this is roughly similar to about ISO640 or 800 on my 5D Mk I. That's comparing in-camera JPEGs from the D600 with LR 4.1 processed RAWs from the 5D.
Major pluses thus far:
» Open aperture metering with AIS lenses—of which I have 4
» Focus confirmation with manual focus lenses
» Dedicated shooting mode dial
» Storable non-cpu lens IDs
» Far more accurate metering than the 5D with manual glass
» Assignable function buttons on the front
» It displays more information in the viewfinder
» Lots more custom options. Lots and lots.
Taken with the Nikkor 35mm ƒ/2 AIS, ƒ/4 at ISO2000.
The Weaver by Nathan Allworth, on Flickr
Happiness is a loaded camera.