I held the D6oo today...
... and I think it feels quite nice. I have no doubts about the image quality and functionality. BUT I think I will save up for longer and get the D800. I am just missing the feel of my D300, and getting the D600 while keeping the D300 as a second camera (with longer lens, as standby) will confuse the hell out of me (I am getting old :-)). I think I am just so used to the ergonomics of the D300 that I will rather wait a year longer and get the D800 (or E).