An image of Mark Zuckerberg, CEO of Facebook Inc., left, with Robert Greifeld, CEO of Nasdaq OMX Group Inc., right, remotely ringing the opening bell for trading is projected on a screen at the Nasdaq MarketSite in New York on May 18, 2012. Photographer: Peter Foley/Bloomberg Few have benefited more from the U.S. bull market that started in 2009 than technology companies, and none are being counted on more by investors to deliver the earnings needed to keep it going.