The rate at which U.S. consumers are going social continues to slow, but that doesn’t mean there isn’t room for continued industry growth.As of May, nearly three-quarters (72%) of online U.S. adults reported using social networking sites -- up from 67% in late 2012, according to new data from the Pew Internet Project.“When we first started asking about social networking sites in February 2005, just 8% of online adults said they used social networking sites,” according to Aaron Smith, senior researcher at the Pew Internet Project.What properties make up consumers’ social diet?Well, as of May, 18% of online adults considered themselves Twitter users -- roughly double the 8% of online adults who said they used the micro-blogging platform in late 2010. Web users ages 18-29 are the most likely to use Twitter.More broadly, social networking site usage is a major activity for Web users from a wide range of demographic groups. Younger adults are especially avid adopters, but social networking continues to grow in popularity for older adults, as well.In fact, six out of 10 Internet users ages 50-64 are now social networking site users, as are 43% of those ages 65 and older.Although online seniors are less likely than other age groups to use social networking sites, adoption rates for those 65 and older have tripled in the last four years -- from 13% in the spring of 2009 to 43% now -- according to Pew.