LOTS of people dress up (Moreso on the Magic than on Wonder). Some people buy costumes off the Internet or ebay, others retro-fit costumes from Halloween/Renaissance fairs. My whole family gets into it big time...we accessorize the costumes with hideous jewelry and chains from the clearance racks at places like JCPenney...capris or cut off sweat pants can serve as pirate bottoms, and there's so much pirate motif stuff floating around now it's pretty easy to find pirate themed scarves and shirts and medallions.
Before dinner on Pirate Night there are photo ops with characters dressed as pirates and also Jack Sparrow in the atrium areas. All the waiters are wearing pirate gear, your dinner menu is on a "treasure map" scroll, and there is a pirate parade during the meal. After the late seating, everyone crams onto decks 9 and 10 where the sailaway party was, and there's a pirate "invasion" with pirates climbing down the masks, an altercation with Capt. Hook, a rescue from Mickey Mouse, lots of music, group dances like the Stomp, and fireworks! Then you can commandeer a sun lounger on deck and watch one of the POC movies on the big screen outdoors. It is HEAVENLY fun.