I'm in New Zealand. When playing D&D, I don't use standard international units, I use the supplied Imperials instead (it's just easier to go without conversion, it's all abstract really). Anywhere else, I'll be using standard metric. Which means I'm going to go back through Twilight and change all the references to 5' squares to 2m squares, which is annoying, but I use the excuse that I was brainwashed at the time. Metric makes everything easier to calculate, anyway - when computing how easy it would be to breach the crust of a world I just designed, I just go, "Hm, x with a couple extra zeroes, yada yada, answer".
(Yes, answering that question is important, even if the answer is "you can never do it".)