Funny. As we all know, you can not teach someone how to boom by telling them. It's a "learn by practice" skill (that's why God invented short films) and I believe that boom operators are born and not trained. Just my $.02.
As for rehearsals, they just don't happen any more. With the allowance of multiple video cameras which cost the same to run, one or five, 30 second take or twenty minute take, and because of that, wireless mics on every actor all the time, directors now just shoot anything that moves. No skill, no forethought, no love for the craft. That's ahy I don't do that work anymore. Sad.
Oh, and rant over, BTW.
D.