The D600 is the first foray in to "Consumer FX" for Nikon. Until recently the cost of producing the FX sensor has been so high as to immediately preclude the idea of a "consumer level" body given that most consumers can't justify spending nearly $3K on a camera. With the D600 they've been able to bring that down to a justifiable cost for the serious consumer, and with the D800 they've given the "pro-sumer" an option as well. As Dave mentioned, the distinction Nikon makes is important as ownership of a D600 will not qualify you to participate in the Nikon Professional program, even if you make a handsome living shooting Nikon. Same with the D7100, though the D300 will qualify you (if you also own a D800 you're good, and your consumer grade cameras will also be covered in the program). I would make the argument that the current sensor in just about every Nikon DSLR is capable of producing professional results, but it's the body construction and the knobs, dials, bells and whistles that makes the difference.