The 16th century had Nostradamus. The 19th century had Rasputin. And the 20th century has...Faith Popcorn? For over 15 years, this soothsayer has been chairman of BrainReserve, a think tank that analyzes and forecasts consumer trends. Usually Popcorn makes her predictions known only to her list of blue-chip corporate clients, but now she's letting us all take a peek at the world of tomorrow in The Popcorn Report. Her list of current and future fads includes ''cocooning'' (''a sort of hyper-nesting''), ''egonomics'' (''a nicer narcissism''), and ''down-aging'' (''40 now is what used to be 30''). Popcorn's corporate benefactors pay untold sums for these visions, so I suppose we shouldn't scoff. Still, the most interesting question raised by this book is never answered is that her real name or what? C

