Thinking in both measurement systems isn't really a problem. It's quite like being bilingual or multilingual, and not confusing at all. When I order fabric from the US, it's in yards, and when I get it here or in the rest of the non-US world, it's metric.
I will admit that I have mental hiccups with temperatures, though. I think in Celsius, and Fahrenheit temps are difficult for me to "translate" into known heat/cold scales. I have to really think to convert someone's temperature of 101 F !