Until now have always adjusted the ISO manually, but this thread has persuaded me to give auto ISO a go. Pleased to see you can set the maximum ISO and minimum shutter speed (when in Av) on my 5D3's auto ISO options (as well as it being fully usable in M), but with my 5D2 it's a bit crap: unless I'm mistaken I can't set a minimum shutter speed, the max ISO is limited to 3200, and in M it defaults to iso400 for everything! I can see the point made earlier that Canon dragged their feet implementing it.
I understand the logic that it makes sense to avoid using it when using flash as the key light source, as it will interfere with the ability to control the amount of ambient light in the shot, but does it work OK when using a touch of fill flash, i.e when you want to correctly expose the ambient light?