The discount PINs are sent via e-mail or postcard, and are specific to a person's or family's name. There doesn't seem to be a whole lot of logic on who gets them or why. And in this economy, there is no such thing as a "normal" discount. We've seen things like "Kids stay, play & eat free", "Buy 5 get 2 free with a $500 gift card", "Buy 5 get 2 free without the $500 gift card", "40% off", "Everyone pays kids' price", etc.
Just keep watching these boards and you'll get information on everything coming out, including any public codes that anyone can use.