I'm one of the few who did not find this movie scary, because of 3 reasons:
1. I didn't see it in '73 when it came out at the movies because I was only 5.
2. I read the book in the early 80's when I was in my teens, so that pretty much spoiled any surprise or shock-value that the movie might hold.
3. I finally saw it after that on television, and by then the delivery was already becoming out-dated (although, to be fair to the flick, and to all who participated in its making, I'm sure if I'd seen it at the movies it would've been different).
I believe the book was written by Shirley Maclaine's (sp?) brother, at least that's what I read somewhere.