Other than personal height and weight and wheel diameter, I never use any non SI units.
What's interesting to me is that the Americans I meet are mostly metric. They are either military (on mountain skills training) or climbers. Those two groups are used to navigating in kilometers (the UTM divides the world into square km) and talk about gear weight in grams/kg, measure food in grams, liquids in liters, ski length in cm, ice axe length in cm, ice screw lengths in cm, boots sole lengths in mm, pack volume in liters, and on and on. We measure peak height in meters, elevation in meters, and plan trips in m/hr of vertical ascent and km/h of horizontal travel.