The flags are still used quite a bit by commercial
vessels, but more as a measure to cover their rear ends. I fly both Alfa and the dive flag during dive op's. As for day shapes, I fly the ball-diamond-ball periodically such as when I have equipment
over the side. I don't expect most people out on the water
to know what it means though. I sometimes get "the look" from sailors who had to alter their course to avoid me.
I really wished people used flags more often, if not anything else, they dress a boat up a little.