I've seen one in my town, Jacksonville, Fl in the last 5 years. It was a 2WD Ural. Saw him at a traffic light.
The only exception is when I took an STEP class, then I saw another one. The class was interesting - it had one sidecar, one CanAm, and one Scooter with a two wheel attachment that gave it a total of 4 wheels, which seems like more of a car not a three wheeler.....
I ride a Suzuki - nothing is up my arse.....
Generally, when riding mine as a 2 wheeler (when I take the car off) other riders wave and smile. When I'm driving it as a sidecar outfit people in cars wave and the other bikers don't...... weird, but just something I've noticed.