In some instances, it makes no difference.
How fast is 150'/rd in mph? in kph? Both are a pain in the neck.
But when you try to figure mass and volume and stuff like that, metric is the way to go.
How many gallons will a 10'x10'x10' room hold?
How many litres will a 3mx3mx3m room hold?
The first question takes a LOT longer to answer. Hell, I can do the second in my head, and I was born, raised, and educated in the states.
If it makes you feel better, call them Scientific Measure... (SI units)