I received one in an e-mail in December, and the e-mail contained a "Book Now" link. I clicked the link, which took me to Disney's reservation site. I entered my planned vacation dates to check availability and was asked to verify my last name and zip code in a pop-up that also had the code already entered. Once I verified the info, the usual results list appeared, showing the resorts/rooms available with the PIN discount. I was able to book both a MYW package and a room-only reservation online with the offer I received.
ETA: My family took our first trip to WDW last March, and ordered a new planning DVD in November. I received e-mails with unique offer codes in April, May, July, August, and December.