The discount is NOT at quick-service spots; it's only at certain table service restaurants during lunch only (11:30 AM – 4:00 PM)
Restaurants included:
Jungle Navigation Co. LTD Skipper Canteen
Liberty Tree Tavern
The Crystal Palace
The Diamond Horseshoe
Tony’s Town Square Restaurant
Akershus Royal Banquet Hall
Biergarten Restaurant
Coral Reef Restaurant
Rose & Crown Dining Room
The Garden Grill Restaurant
Hollywood & Vine
Mama Melrose’s Ristorante Italiano
The Hollywood Brown Derby
Tiffins Restaurant
Tusker House Restaurant
Ale & Compass Restaurant at Disney’s Yacht Club Resort
ESPN Club at Disney’s Boardwalk Inn
Grand Floridian Cafe at Disney’s Grand Floridian Resort & Spa
Kona Cafe at Disney’s Polynesian Village Resort
Olivia’s Cafe at Disney’s Old Key West Resort
Sanaa at Disney’s Animal Kingdom Lodge
The Wave… of American Flavors at Disney’s Contemporary Resort
Whispering Canyon Cafe at Disney’s Wilderness Lodge
They randomly up the discount throughout the year but it's always unexpected, and tends to be done when they are trying to drive more traffic to restaurants. The last increased discount was back in January, I believe, but it included different restaurants (and may have been dinner only?).