How casually glamorous is Gore Vidal's Point to Point Navigation, his follow-up to his delicious 1995 memoir Palimpsest? Francis Ford Coppola thanks the author for turning him on to wine, and Johnny Carson, out of earshot, shares the secrets of comedy. Meanwhile, Saul Bellow fails to stay single: ''He had, by the end, five wives, I think, and since they were all so alike I never put their names to memory.'' Also, Garbo speaks. Vidal, ever the aristocrat, isn't bragging; that's just life. The volume is a disjointed contraption built to salute old movies, reheat ancient gossip, and run bizarre errands pinning, for instance, the JFK assassination on the Mob. It's random. Nevertheless, the story sings when Vidal turns to memorializing his late partner, Howard Austen. Those passages are as insightful as the stunned mourning of The Year of Magical Thinking by Joan Didion, whom Vidal here dishes about as the possessor of ''the most endearing scowl.''