You've been in Japan too long when, while back in the U.S., you're asked your shoe size and reply, "Er, 26 centimeters?" One of the first things to go after moving to Japan is forgetting your shoe size in your home country's system of measurement, and whenever I'm buying shoes while back home I find I have to try on several pairs to find ones that will fit. Like most of the world, Japan uses the metric system for measuring distances, and it's surprisingly easy to get used to using kilometers and centimeters, just as getting used to temperatures in Celsius takes only one instance of being cold because you didn't bring a jacket due to not knowing that 16 degrees was jacket weather. In lieu of paper sizes like "letter" to "legal," the Japanese use the international ISO standard, which takes time to get used to but is very logical -- A4 is similar in size to letter, A3 is twice that size making it similar to tabloid, and so on. Japanese plugs are the same shape and voltage as used in the U.S., but they almost never have the third prong for a ground (or aass as they say in Japanese, the local pronunciation of the English word "earth"), and this causes you to get pretty savvy about carrying a plug adapter with you in your laptop bag. Finally, there's probably nothing taken for granted less than paper coffee filters, but they're quite important to us: the large filters are not available in Japan, so if the J-List crew wants to have our morning coffee we need to plan ahead and bring them over from the U.S.
Living in Japan will make you forget your shoe size.