It is going on until right after 4th of July (I think it ends on 7/5). It's a surcharge the regular price. I haven't been able to find a site that shows the specific surcharge for each restaurant, but from what I can gather it's about $4-$5 for adults, $2-$4 for kids.
Allears says these restaurants are affected:
Boma Breakfast and Dinner, Cape May Breakfast and Dinner Buffet, Chef Mickey's Breakfast and Dinner, Trails End Buffet, 1900 Park Fare Breakfast and Dinner, 'Ohana Breakfast and Dinner, Captain's Grille Breakfast Buffet, Tusker House, Garden Grill, Princess Storybook Dining, Crystal Palace, Liberty Tree Tavern Character Dinner, Cinderella's Royal Table, and Play 'n' Dine at Hollywood and Vine