Hmm.
DistanceMiles & yards for travelling, cm & mm for measuring things properly, but inches for a quick estimate!
HeightFeet primarily, but pretty good at working in metres now
WeightKg & g. And stone!
TemperatureCelcius when its cold, Fahrenheit when its hot. Err...
LiquidsPints for alcohol, gallons for fuel, litres for drinking water!
AreaAcres and square feet. Oh, and football pitches of course...
I'm sure there's some logic in there somewhere....
...actually, I doubt it.