“This summer, movies such as ‘Bruno’ and ‘G.I. Joe’ have had unexpected tumbles at the box office — just within their opening weekends — while ‘Transformers: Revenge of the Fallen’ survived blistering critical reaction to become a blockbuster. Box-office watchers say the dramatic swings might be caused by Twitter and other social networking sites that can blast instant raves — or pans — to hundreds of people just minutes after the credits roll.”