I have the 24-70 f/2.8, and it is indeed a great lens. However, in reality, it's the least used lens I own. I find I usually have the 24-120 f/4 attached to my D800 instead because it has more versatility, is lighter and more compact, and it has VR. I very seldom ever wish I had the extra aperture stop for the type of photography I do, and I don't mind bumping the ISO up a little if I need to regain some shutter speed. When I want to shoot the occasional portrait or other subject matter where I want nice bokeh, I usually just use my Zeiss Makro-Planar f/2 anyway. Apart from the 24-120 having more distortion, which I can correct in PP, I truly can't discern any IQ difference between it and the 24-70 at the same focal lengths. So, I might as well have more zoom range and VR in a smaller, lighter package. The 24-70 certainly has a more solid build, as if it might last forever, but until I break my 24-120, I have no reason to suspect it won't hold up to many years of use.
I'm actually thinking of selling my 24-70, in fact; not because there's anything wrong with it, but because I just don't use it much.