Has talk-show powerhouse Oprah Winfrey just switched her loyalty in the e-reader wars? Winfrey, who helped launch Amazon's Kindle with an early endorsement, gushed over Apple's iPad on a recent episode of her show — singling out an app that lets the iPad mimic the Kindle: "You can take all the books from your Kindle and put them on your iPad." A spokesperson later clarified later that Winfrey uses both devices. If history is any guide, a rave from Oprah (whose book club is a publishing phenomenon) will boost iPad sales, but Amazon executives aren't worried, saying they welcome any device that drives sales at Amazon.com. Watch Oprah exult over the iPad: