Fab.com, an e-commerce site that saw a surge in revenues of 550 percent last year and its membership base jump from 1.5 million to 12 million people, has found customers using mobile apps deliver twice the lifetime revenues of those on its website.Related StoriesQ&A: Apple takes on TVTwitter pulls plug on TweetDeck for Android, iPhoneFacebook does damage control after claims of rigged News Feed
