Though recent studies show that Twitter has been growing exponentially, more than 60% of US Twitter users fail to return the following month, reports the Business Insider (via MarketingVOX).Twitter’s growth has come, in part, as a result of celebrity exposure, which fueled a record number of people to sign up in March. However, Business Insider said it faces an uphill battle keeping new users interested. Yesterday Oprah - who vouched for Twitter on her show two weeks ago - made headlines when Silicon Alley Insider observed four days have passed since her last tweet. Shortly after users speculated whether the high-profile talk-show host was already “over” Twitter; she began updating in earnest again yesterday. Read More»