Yum... I'm going to rent this movie as soon as I can just because of that S&M beehatch. 
Yeah, don’t listen to the sissies. It is a good movie.

There seems to be a tradition of depicting piano teachers as insane in movies

. Here are a few more besides The piano teacher:
The seventh veil – A concert pianist played by Ann Todd tries to commit suicide, she then goes on therapy with Herbert Lom, who uncovers that her problems can all be traced back to her sadistic piano teacher (James Mason), who amongst other things beat her fingers with a stick when she made mistakes.
The 5000 fingers of Dr. T – Piano teacher Dr. T, runs a piano school whose main aim is to make 500 boys practise the piano 24 hours a day, 7 days a week.
Madame Sousatska – Shirley Maclaine as a frustrated piano concertist who insists on Hanon for her charges.
Best wishes,
Bernhard.