I shoot with the other brand - and I have had extensive experience with their 1Ds Mark II.
Yesterday I got to spend ten minutes with a brand new D2X. As much as I've been on the Other Side of the Canon vs. Nikon debate, there's something that needs to be said about a professional camera I can pick up and simply and intuitively use without having to refer to a manual.
The Canon requires a manual. You have no hope of using it without one.
A few notes:
* Sharpness - the D2X's sensor is capable of resolving much more detail than the Canon. Every review I've seen even with Canon's L-series lenses have shown the 1Ds II to be soft in full-crop. This is a good idea for Nikon as high speed crop
mode puts a heavy burden on the detail that the sensor can resolve. Perhaps I wasn't using the *right* L-glass though...
* Not full-frame - while I appreciate and like full-frame shots, vignetting is a big problem on full frame digital (and film) bodies which the DX format seems to resolve. A 28mm lens on DX doesn't give me the wide angle I enjoy, though.
* Viewfinder - Take a look through a 1Ds II's viewfinder and then compare with the Nikon. I think the Canon's viewfinder wins hands down.
* Screen - ... however, the Nikon's 2 inch screen is amazing. Colours are brilliant and it lets me zoom in enough to check sharpness on the go. The Canon's screen lets me zoom in pretty big although the edges are blurred for some reason. After putting the camera down, the thought running through my head was "wow.. the screen".
* High ISO noise - I hate to say it, but the Canon's high ISO noise is appreciably better than the D2X's. Colours in the D2X seem a bit more *there* than the Canon at high ISO, though. I look forward to putting some images through severe noise reduction and seeing how they turn out. ISO 3200 is close to unusable without post.
* Image colour - the dynamic range of this thing is incredible but doesn't really leave the Canon for dead. It's a personal thing, I guess -and I'm still of the Canon camp.
* Weight. Lighter than the D1X *and* the 1Ds II. This makes all the difference when you are holding it with a light lens.
* Handling - I prefer the handling of the 1Ds II in terms of how it feels in my hand but the reduced weight of the D2X is really lovely. Big improvement from the D1X, too - grips feel a lot nicer than the D1X but the vertical grip on the 1Ds II is my preference here.
* User interface - love the layout of the controls. Easy to use! One button to set the ISO - *one*. The Canon required two buttons *and* the turn of a wheel -simultaneously. Sheesh.
* High speed crop
mode. Rocks. That's all I have to say about that. There's nothing like that machine gun sound coming out of a DSLR. Solves the "I need a 1Ds II and a 1D II in the kit" problem - or the "I want the good lens on the other camera" and not have time to do a swap.
* Accurate battery indicator. With the Canon, I shoot 1000 images, bar drops down to 50% and I get five more before it tells me to replace the battery. Thanks. The Nikon seems to give me a more gradual battery indicator which seems more representitive of the actual battery charge. Smaller battery size! Nikon claim 2000 shots I think? Wow. Batteries are small which means they *fit in a pocket* ready for quick changeover. The Canon batteries fit in my pockets... if I wear cargo pants or a big coat. Canon batteries appear to be cheaper, however, but I may be wrong.
* The little dash of red on the camera. The Nikon looks less serious and more 'wow'. The Canon has gold plated "1Ds" and "Mark II Digital".
* I'm told the D2X is not weather sealed? This is a must-have for some pros who shoot in the open - if it rains, there goes your shots. It was funny to see all the Nikon shooters run off to shelter when it started raining at the Airshow Down Under this year while all the 1-series Canon users continued shooting - some of them pulled out their raincoats though.
* Price. I really don't need to say anything about the D2X coming in at almost half the price of the Canon. I originally thought that the Canon's price could be attributed to the included software (I tend to use CS2 + ACR anyway) and their service ...but after my recent experience (see below), I'm in doubt.
I haven't seen many pros shoot above 800. In fact, I've rarely see anyone shoot above 400. I prefer available light shooting, though.
If you're a diehard Canon user and you feel enraged for me letting the team down then ask Canon why fixing a shutter bounce problem takes five weeks with a 1Ds II for a non CPS member. That's no way to treat a customer.
I can't help but see the feature set of the Nikon and wish that the Canon had those features. As for the replacement to the D2X, the sensor resolution and noise are the only two improvements that come to mind.
Conclusion: Ten minutes with a D2X has really spoiled the 1Ds II for me - I'll miss a lot of features when I pick up that Canon again.