I hate this American feet system too. It's the most retarded counter-intuitive bs system that 'merica is too stubborn to change. But then again, I think its too late to change because doing so would simply create massive chaos and confusion.
Most people I know use metric and American systems interchangeably, the one that throws me for a loop is the Imperial system of weights and measures. Watching UK police procedurals and hearing terms like; "..the suspect is a middle-aged man, about 14 stone in weight..." just causes my brain to blank out.
I do think it depends on the industry, though. I use a lot of mechanics tools, and have pretty full sets of both metric and ANSI sizes. But when I used to be a carpenter, it was all feet, inches, and fractions.
To add to the mix, I work in telecommunications, where we have different types of "standard" cabling. A T-1 is a standard high speed data link for cell sites and corporate WAN infrastructure. It can carry up to 1.544 megabits of traffic each way, on 24 64k channels, or as a combined pipe. E1 is the European standard; 32x64k channels, 2.048Mb in capacity. My company sells planning software that has to accommodate both standards, and display them accordingly on reports, so we spend a lot of time figuring out conversion issues.
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When I was in grade school we still had to know units of measure like rod, chain, and league. And peck, pint, bushel, etcetera, etcetera... Fun stuff!