Now that there is no 5D mark II until at least October I am still riding the fence on waiting or purchasing a 1Ds Mark III. (Who knows, the 5D may be discontinued, as it may have been a full frame stop-gap until the FF 50D!)
The features of the 1 series that really appeal:
1. Actual weatherproofing (not usually needed, but on occasion.)
2. 2 Batteries built in, with smooth casing (vs. add-on grip)
3. 14-bit images
4. 3 inch screen (40D has #3-4, but I don't want a 1.6x crop for my main body)
5. Individual lens custom autofocus.
6. Big blowups (I like doing 20x30 prints and might do 24-36 if I could retain quality. I haven't tried with my 5D)
I fully understand that some of these things are purely luxury wishes and won't change image quality. But heck, I'm a guy who upgraded from a Rebel XT to a 30D (same sensor!) just because of the bigger screen and heftier grip!
#5 is the one that is making me consider a 1Ds so strongly. My 24-70 doesn't focus as sharp as it should but with a 1 series camera, I could make have the camera recognize that lens when mounted and compensate for any back or front focusing.
I have even thought about getting a 1D Mark III but then crop factor and lower MP (don't lecture me, I know the deal) both creep back into my mind. The high cost would be a stretch, but not unattainable. I look at it as a "lease" of sorts. If I buy at $8000 and sell in 2 years for $7000, I just need to get $1000 in gigs or consider it a $500/year rental.
Anyone who has a 5D, 1D, or 1Ds have any words of wisdom? I am happy to be swayed in any direction!