Anyone recommend the grip with the D600 and why?

where the D300/700 common grip (MB d10) makes those cameras a little large, the D600 with its grip (MB D14)  is a perfectly sized camera for me, and makes handling the 2.8 zooms a breeze. Of course you still have the option of going grip-less with the kit zoom or a small prime, and the camera in that disguise is much more discreet than its bigger Full Frame brothers - best of both worlds.

I am getting a Kirk L-bracket for the gripped 600 - can't wait.

Also, the D600 gets really good mileage out of one En el15 battery, and goes all day on two ... better than my D700 with grip, and the 700 is pretty good.  I think you have to rate the 600 energy efficiency as excellent.