I will add comments on my first impression here as and when I have spare time (I do not have the writing or analytical skills of Gordon, so please do not expect anything other than some basic opinions on this camera). I have a fashion shoot this weekend where I will use the new camera (assuming it works fine with my strobes/triggers which I will test this evening). I hope it will go well. I will post some of the photos of it once complete and edited.
For now I like:
-AF (hard not to like after using the 5D2 AF for so long) - seems spot on so far, I am really impressed
-viewfinder - big and bright
-build quality - feels more compact and solid compared to the 5D2
-ISO - just wow. I think this is something that the Nikon guys have been enjoying for a while. Love the high ISO quality
-silent shooting - though having a big camera does often draw attention when out shooting in the street, if they do not see you the silent shutter does ensure that they will not notice you due to the loud clunking. This is also going to be so cool for weddings. The clunk of the shutter is definitely unwanted in a church where it really seems to stand out.
-picture quality - so far so good. The standard JPEGS are great and the raw files seem fine; though there are bugs with DPP at the moment and LR does not yet support the 5DIII
What I do not like:
-mode lock button - this is a pain. I was happy with no lock on the 5D2
-picture preview zoom - you need to hit a zoom button then use the scroll wheel by the shutter release button - a pain but I guess I will get used to it
More to come when I have used it more. A couple of shots below. I will add more tonight or tomorrow night when I have time to process them.
This one was from a raw. ISO 8000(you can check the full exif on flickr)

This is a jpg from the camera, processed though LR4. Full exif on flickr.
