I had it happen (ball-lodged-beween-rim-and-backboard) earlier this year, actually. I didn't actually see HOW it happened (I was the L, so I was watching the rebounding action), but it did happen.
I also caused a ball to rest on the flange during a FT attempt in my JR High playing days. Also had a teammate who, airballed the first of 2 FTs. Coach said "You need to shoot it a bit harder", and his next attempt went over the backboard.