I just love how most people act as if swapping camera brands is such a simple task. I briefly considered switching to Nikon when I heard the price of the 5D3 (Very briefly, in my head, never made a post on the forums, mind you) as I was not too thrilled with Canon at that point.
I too have only been doing this semi-pro for about 4 years. But do you have any idea how expensive it would be to make the switch to Nikon? Canon 5D3, 7D, 70-200 F2.8L IS II, 24-70 F2.8L II, 100 F2.8L IS Macro, 24-105 F4L IS, Sigma 35 F1.4, 85 F1.8, 50 F1.4, Tokina 11-16 F2.8, 4x 600EX-RT, 2x 430EX II, 580EX II, 3x PW Flex TT5, AC3 Zone Controller... and I'm sure the list goes on with other accessories and random crap I've accumulated over the past few years. And my photography career is comparatively short to many of yours.
It would literally cost me thousands of dollars to make the switch to Nikon, for an imperceptible difference in image quality. In the end, it was much cheaper just to suck it up and purchase the 5D3, rather than wasting all that money switching brands. And I love the 5D3 now =) It helps that I got mine about a year ago for $2700 rather than full retail.