Interesting, unpublished fact: you can use leftover days on a Walt Disney World Hopper pass at Disneyland or DCA! This is probably because Disney World Hopper passes cost much more per day than Disneyland passes, so Disney is actually coming out way ahead on the deal. Present the WDW Hopper at the gate on arrival -- they will take it somewhere, deduct a day from it, and give you a one-day pass. This information was confirmed as of April 2004.