What a fun thread!
To throw my 2 cents in, I was trained as a Civil Engineer, with a couple of surveying courses thrown in in the USA. For the last 20+ years I've worked on a military base in Germany. So I've learned English inch, foot, yard, mile, Surveying chains, rods and furlongs, and metric millimeters, centimeters, meters, etc.

I have tape measures with both metric and english and I have to say that doing small projects around the house I use metric exclusively! I'll never go back to inches and fractions.

However, when talking to Americans over here I use english measurements and with Germans I use metric. It is almost automatic by now. Just like I use my fork in the right hand eating on-post, but in my left hand off-post.

Multi-culturism is wonderful. I can have a "Senior Moment" in 3 languages and 3 measurement system!