The hour is 11:30 on this Saturday night aboard the American Queen, somewhere south of Natchez, Miss. The dance floor in the Grand Saloon is deserted, and a lone man sits in the 24-hour Front Porch lounge, reading a paperback novel. The evening's holdouts, perhaps 30 people who, like most of the passengers, appear to be 55 or older, are in the Engine Room Bar. Jackie Bankston, who plays the piano, and Bob Schad, who plays guitar, are singing the '70s Kenny Rogers song "Lucille," which has roused these last-to-bed passengers into a sing-along. Only one couple is dancing, laughing...