Psychologists agree that the ability to concentrate is key to achieving our goals. But today's high-tech world is full of distractions, from thousands of cable TV channels to millions of internet sites, with smart phones constantly within reach. Some experts say our attention span is actually shrinking. So should it be any surprise that Americans have fallen in love with Twitter, the online social networking and "microblogging" site that lets users send and read "tweets" limited to no more than 140 characters?
Twitter attracted confusion (and no small amount of scorn) when it debuted in 2006 — co-founder Jack Dorsey admitted that the service is "a short burst of inconsequential information." But there are now more than 200 million "monthly active users" posting more than 500 million tweets per day. Singer Katy Perry currently has the most followers, at 46.8 million. She's trailed by