Two things:
Number one, if someone asks me what the rulebook says, I'll respond if I know the answer.
Number two, if I know someone is breaking the rules, I'll open my mouth if the infraction gives that player a distinct advantage.
If someone breaks a rule unknowingly, and it doesn't give him an advantage, I'll usually just let it slide for two reasons. Number one, I don't want to be known as the rule nazi. We have one of those in town, and everyone knows who he is. And everyone hates playing with him. And number two, if I corrected every rule infraction that I saw on the course, I'd still be playing my round from Monday morning.