My instructor mentioned to me one day that she has provided feedback to people before, but they continue to ride the way they want to (old habits die hard). Some people seem to go to spin class just to get in their exercize for the day, and they aren't concerned so much about their form. So I can't say that mentioning anything to them yourself would do any good (although tempting as it is ) I must say there are some interesting ways to ride out there!!!
I wonder what others think of the way I ride?