Yet “iDisorder” is a pleasant surprise — lean, thoughtful, clearly written and full of ideas and data you’ll want to throw into dinner-party conversation. Did you know that psychologists divide Twitter users into “informers,” those who pass along interesting facts, and “meformers,” those who pass along interesting facts about only themselves? Or that 70 percent of those who report heavily using mobile devices experience “phantom vibration syndrome,” which is what happens when your pocket buzzes and there’s no phone in your pocket? (I thought I was the only one.) Or that heavy use of Facebook has been linked to mood swings among some teenagers? Researchers are calling this “Facebook depression.” (And I thought that my children were just having a lot of bad days.)