Two points about carb heat, specifically on the R22 which is where 99% of my low heli time is.
1. Maybe this is splitting hairs, but it's not the gauge which is ineffective under 18" MP - the power settings are low enough that the butterfly is closed enough to present a MUCH larger risk of icing. I seem to remember from the safety course that a stude and instructor had an engine fail while doing a practice EOL during flight, and successfully put down. The Chief Pilot was just as surprised when his engine quit just after he started his descent to the field the other helicopter was in. So - Carb ice below 18", and although it's not in the book, plan to apply it well before you lower the lever.
2. When I learnt in Oz, carb heat wasn't a real risk. I wasn't taught even to include carb heat in the checks as a "point to consider" - this puts me at a huge disadvantage as it's not instinctive to think about it, although it is getting better. Anyone found my post-it which I've left on the MP gauge after I've flown it ? This is a big issue for me - last thing I want is to kill myself because of an omission by thew guys who taught me.