the 1D Mark III has a Safety Shift option to automatically increase the ISO speed whenever the maximum/slowest aperture/shutter values are reached. the applicable ranges for aperture/shutter speed are set by the user in the camera's preferences and the system works great. it's really nice to be able to take a picture without worrying if the ISO is high enough.
I usually shoot in Av mode and my one quibble with the Safety Shift system is that the fastest value for the minimum shutter speed value is too low. it's currently 1/60s and I frequently find myself in situations where 1/60s is too slow. 1/125s would be much better in many situations and 1/250s would sometimes be the most suitable value to use.
if anyone has connections at Canon; eg, beta testers; please make a formal request that they increase the fastest value of the minimum shutter speed value to at least 1/250s in the next firmware update.
regards,
Gregory