I remember when all hotel keys really were keys, and they would come with an enormous key ring, designed to dissuade you from taking the key out of the hotel - leaving it with the receptionist on the way out. I'm sure that one time when I was little we stayed in a hotel where the key rings were made out of a huge slab of blue plastic which had the address of the hotel on it and a little square in the corner where you were supposed to put a stamp if it needed posting back to the hotel!
At WDW, the key to your room can be used for lots more than just opening doors - it can also be your ticket to the theme parks (although not for us last time as we bought annual passes) and a charge card to be used all around the World. I've still got mine from August tucked in my wallet, and every time I pay for something with a credit card I am reminded of my holiday.
It'll probably still be there when we go back in December - exactly 100 days from today.