At the last local pro photographer meeting, one chap argued that the camera was irrelevent, as clients never asked what you shot on and he'd never not got a shot, because of camera limitations.
Well I'd argue otherwise, I was able to get shots on one job, another colleague failed to, as I had full frame and good high ISO [5D] and his D2X struggled both with shutter speeds, lack of fast apertures and with wide shots.
The D3 has levelled the field since, but at the time, I could only have used a 5D or a 1dsIII to get the shots.