I don't know what to say about America's obsession with Inches and Gallons, except get with the program already.  Every other country in the world has done it, and the US does it for important things.  (Like science and medicine).  So, for example, Celsius is used at the hospital and in science class but not for the weather?  Seriously?  Also, why is Milk measured in quarts, while soda is measured in liters?  Ah, the mysteries of America.

If you're a foreigner coming to Japan, you might find nostalgic comfort in Irish pubs or your favorite foreign restaurant, or even my renting American movies.  You are just too out-numbered with it comes to metric though.  Even most foreigners you meet will be from countries using metric, and so you are just going to have to deal with it.

It seems most Americans know liters already, so that may not be a big deal.  People seem to get acclimated to distance and even mass quickly, yet for some reason, everyone seems to have problems with temperature.  I'm not sure why this is, but if you are planning to travel to Japan (or.. anywhere, really), start looking at the temperature in Celsius every day before you go on your trip, so when you see that the temperature is 30, you will know that's not coat weather.