I just shot a fashion editorial Monday and used the 1D Mark III for the shoot. I planned shooting available light/tungsten light since part of the shoot was in a concert club with a band. I shot at 800 ISO all day, usually around 2.8 to 4 at 1/60. (98% of the time, I shoot 100-200 ISO.) I'm very impressed by the low grain/noise generated at that speed -- easily equal to about 250/320 ISO on my 1Ds2. We're still editing through images, but I viewed most images with Canon DPP and I'm impressed by the resolution as well. Normally, I use Lightroom or Camera RAW or Capture One. However, lately, I haven't been as happy with Lightroom for some files -- images seem a little noisier and not as sharp.
If I have a chance, I'll post a few shots to show sharpness, detail and grain. I'm very impressed with the camera's performance. Hate the new menu system -- with a passion -- but love the results.