Mark, I'm a wedding shooter who regularly shoots with my camera in hand or on strap for 12-13 hours straight. I don't have to worry about rain, I only ever use the center focus point, try not to drop it and shoot 95% of the time in manual with auto flash. For me the 5D, as long as it has FF and at least 11megapix of resolution, is a better solution than the 1Ds, ####, until I went digital I was shooting weddings with two Elan II's and that was good enough. Weight matters.
For me it's an ideal solution, however it is kind of stupid that a pro body like the 1Ds could be considered inferior to a 20D like body just because of the chip, didn't work that way in the film days and is still topsy turvy.
I seriously wanted the 1Ds to be my camera body for the next 5+ years. I thought I would be getting at least a 10D but with higher res and FF.
It was really hurting to find out just how bad the noise was, how slow and unclear the review was, how bad the banding in the blacks, how bad the battery life and heavy the batteries and just how bleeding heavy that beast is with a 24-70L and flash after 4 hours.....
But, I learned to get my exposures right each time, to trust my meter and not need the review and I was ok with everything but the weight. The resolution was not a factor, I wish my technique matched what that beast can do (it can't).
This 5D could be the camera that gives me the next 5+ years.
That said, if I was primarily a landscape or wildlife shooter, if I needed to trust my body implicitly wherever I go, be it to the football game or to Nambia I wouldn't think twice, the 1Ds would be it. Luckily wedding shooting is far more 'civil' to camera gear.
I was shooting pics of the 1Ds for ebay in a friends office earlier. He's a journalist shooting with the D70s and Fuji S2. He has pictures in national newspapers about 3-4 times a week as well as shooting more weddings than I do. He tried my 1Ds with lens and flash in his hand, gave it back and said that he would go mad having to hold that for even an hour of straight shooting....
BTW I was using his D70s to take the pictures @ 400iso, the noise on that thing is worse than my 1Ds and the camera seems to be sharpening the RAW's slightly as well, oh and my eye is hurting from squinting down that really tiny viewfinder, hey ho for FF!
Bye Bye.....