Metric weights and measures are also superior in that they are interchangeable; a litre of water weighs a kilo--how nifty is that?

The American weights and measures system is older than the Imperial system (like yankee spelling, they came with the original English settlers). They are sometimes referred to as 'common measure' and you see them usually in cookery: cups, tablespoons, teaspoons etc. Damn handy if you don't own a scale. Bit dodgy for baking though.