AP's include a number of discounts. I've listed the 2004 discounts below, but they expire Dec 31,2004 and new discounts will apply beginning Jan 1st. However note that between 2003 and 2004 there were very few changes and 2005 will probably be similar.
Admission to all 4 theme parks.
PAP also includes Water Parks, PI, DQ, Wide World of Sports (excluding special events)
Passholder e-mails
Mickey Monitor newsletter (4-times annually) which has specials and seasonal items.
Ticket discounts for your friends and guests ($4.00 adults, $3 kids) at PI, DQ, Water Parks
Various WDW hotel discounts (announced periodically)
Food: WDW resorts, generally 10% lunch M-F (They list 9 different WDW resort restaurants)
Food: Epcot, 10% lunch M-F (They list 12 Epcot restaurants which include the main countries, coral reef, and garden grill)
Food: 10% anytime All Stars Cafe
Food 10% lunch/dinner Wolfgang Puck
Food 20% House of Blues (prior to 6:00 pm); 10% off merchandise
Food 10% Planet Hollywood, 10% off merchandise
Food Rainforest Cafe at DD 10% 11:30 - 4:30; at AK 10% 2:30 to close; 15% off merchandise
Portobello Yacht Club at DD, 10% lunch/dinner
Fulton's 10% lunch/dinner
Note: Some of the above restaurants discounts are for passholder and up to 3-guests while others are good for your entire party.
Leave a Legacy, buy one get one free
Virgin Megastore, 10% off
World of Disney, 10% off (some exclusions such as tickets, film, food)
Eurospain 10% off
Tours: 15% off WDW tours. (3 tours at MK; 9 at Epcot, 1 at MGM, 2 at AK)
Golf: 30% day visitor rates, restricted tee times, reservations
Minature Golf: 50% for passholder and 3-guests at Fantasia Gardens and Winter Summerland.
Grand Floridian Spa, 10% off one treatment per visit
Richard Petty Driving experience $20 off regular, $35 off the Package
Sammy Duval water sports at Contemporary, 10% off parasailing, water skiing, wake boarding
Any WDW resort marina: Boat rentals, 15% discount.
Car Rentals: Alamo up to 20%, National varies (use discount code)
Hope this helps.
Bill
Edited to add: Also, the AP gives you free parking at all the theme parks. This is regardless of where you are staying so if you stay off-site, you still get free parking.