I use imperial to annoy certain people
Being Dutch, it's pretty much all metric. Except for TV / monitor and pants (jeans) sizes, those are imperial. And some bicycle parts, diameter of the stem and tubes (1" top tube is standard, 1 1/8" is oversized etc).
When I'm tired / want a ride to be over I "countdown" the last 6.4km in miles. Yes, seriously.
I don't have distance or speed on the main page of the Garmin, though I have a secondary that shows various stats like average km/h, total distance (km) and distance left (km) for the current track (which is usually the next control).