When we went we were given a photopass card that had a 20% off coupon on it. It was in the "birthday card" my DS got from Mickey in our room.
Did I remember to use it to buy a picture.... NO, why??? Because I am an idiot. In fact, I didn't get our picture ordered in time... I went on the day AFTER the photopass expired.
Other than getting one while at the park, I don't think I've ever heard of anyone having one. Good luck, that 20% would be a great deal on a book!