I'm pretty sure I'll be getting a 5d3, but not for a couple of months yet, as I want to read a few non-biased reports about it first and let Canon get some of the bugs out of it with the second or third batch they manufacture.
Some years ago I decided to go to the Canon system, mainly because I thought there was a better choice of lenses and the lenses were a bit cheaper than Nikons.
As far as the camera go, Nikon have some better features than Canon, but then again, the Canon cameras have some better features than Nikon, so it is really just a moot point as far as I'm concerned as they really are pretty equal on a model for model basis.
Hearing all these people whinging on about changing brands because this new model doesn't have what they think they need is really pretty frivolous in my opinion as wasting your investment in lenses and accessories just because one camera has a higher megapixel count, or has USB 3 instead of USB2 is just nuts.
Just as a difference of $500 on a $3K body over the 3 or 4 years you'll be using it is pretty silly too and you would lose far more than that by having to sell all your accessories and buying new ones to replace them.
You often won't find out why there is a $500 difference in the cameras until you really get to know it, and then you might realise that the extra $500 was well worth it as it is more solidly contructed, and the low light performance is spectacular, and to me, having a useable 25,000 ISO as against 6,400 would be well worth the extra $500.