Only those three last bastions of freedom and the right to choose, the United States, Liberia, and Burma, still do not use the Metric System. Until now, one could justify this on the basis that the
Imperial American system was human scaled, based on our body's dimensions and things we naturally understood. (Like 0 is really cold and 100 is really hot, who cares about water boiling and freezing?)
Randall Munroe to the rescue, with his guide to getting a feel for metric, full of universal cultural touchstones that everyone can relate to, like the volume of Summer Glau or the length of a Lightsaber. This should be on the wall of every classroom in America.
In all seriousness, the new green economy will be built on the metric system. Right now the world's wind turbines and photovoltaics are built in Germany and Asia to metric standards. If America is going to be part of this international trend, it is going to have to be part of the international standard. Learn it all from XKCD
It's A Good Time For America To Go Metric
Forget Metric or American Measures, Just Be Sensible