In my experience (Delta Diamond two million miler), security at LHR, CDG, FCO, PVG, BKK, ITM, KIX, HND and NRT always require it to be removed.
In the USA, I have never been asked to remove it at any airport (but 90% of my flights are to Asia or Europe)
On the other hand I haven't had to take my shoes off at any non-US airport.