Hey Navi,
As an owner of the Canon 1Ds MKI and MKII, I'd be willing to bet that the MKIII will be outstanding. It even has 14 bit depth.
I want a digital back so I can do view camera stuff. My main thought is to shoot architecture using a normal lens, but slide the back to get a wide view (stiching them together digitally) without wide angle lens distortion. I'm not convinced that you can pan a fixed lens camera and stitch and get the same effect, as you are changing the perspective.
I'm much more of a technician than a creative, so I think architecture is an area I can get some solid work.
If you don't have that need, then the Canon should flat out kill. Other than their somewhat clunky interface, I think Canon rules the high end digital SLR market.
regards,
joe