I have 2 D700's and they are my primary cameras for working. I had an evaluation D600 for a month, but at the end of the day I wouldn't buy one. There are a still a few things the D700 is better at like AF area, build quality, fps, etc.
I will eventually replace them, I'm just waiting for the right camera. We'll see what CES/PMA brings or their usual announcement later in the summer. But I won't upgrade until we see a 24mp D4 type camera.
I have had one client "complain" about my using a DSLR, more expecting me to show up with a Hasselblad MF Digital. They were more than happy with the images, but when I showed up next time with a rented H3D, he smiled and didn't even bat an eye at the increase on the invoice