How do you like the 5D otherwise?
First canon camera I owned (D60,10D,1Ds,5D) that exposed properly in Av mode. My auto flash is also spot on which makes me think that the iso is accurate for once! The WB is also the best I've ever seen from a canon camera, even ambient+flash is spot on. I would trust this camera to shoot JPG if I had to and I'm a hardened RAW fanatic! The DR is much better than I've seen, I'm not having to compress highlights to get a film like response for portraiture which is unusual. The colours are also far better for me than with the 1Ds, I don't see a need to custom profile which was a necessity with the 1Ds.
Jaggies are visible on angled lines when viewing at 100% in either ACR or DPP, quite annoyed about that, hopefully the fully supported next version of ACR will deal with that.
To make the most of the noise advantages you still need to expose to the right, the noise is similar to my 10D, BUT, the 100% of the 10D and 5D are vastly different, i.e. you would need to print much bigger to notice noise you would have seen on a small print from the 10D. There is thank G-d no banding in the blacks like the 1Ds was plagued with if you underexposed even slightly.
RAW images still take about 2 secs to come up for review though they are instantaneous in playback. Bit disappointed in that. Zoom is smooth and fast and the joystick is a pleasure to use for playback. Writing to the Sandisk Ultra II is so fast I hardly notice it.
The AF points are far too close together and could be marked better, in low light it's hard to diffrentiate between the thin squares. I'm seriously thinking of marking the center one with a pencil if I can confirm that it won't screw up the metering. AF is fast though for low light I've never noticed a difference between the 1Ds and 10D, the D2X defines what fast low light AF is! Choosing AF points with the joystick is easy enough. Press once for center point, again for auto choosing, wiggle to choose an individual point.
Battery life is disappointing, I'm not counting on much better than the 1Ds/10D which isn't good, no doubt the huge screen takes its toll, ditto the larger mirror. Still no excuse though.
Viewfinder is a FF viewfinder, can't say it's noticeably any better than on my Elan II, eye relief is crap for glasses wearers like me (isn't that all modern SLR's?). Lot better than a crop viewfinder though.
The resolution is absolutely fantastic but at higher iso's make sure the exposure is correct as the resolution goes down hill very fast with underexposure from iso800+
Other than that, it's a 20D with FF and better ergonomics, nuff said.