Half of all adults in the U.S. and 83 percent of younger people (18-29 age) said they use a social media site, according to a survey done by Pew Research Center.

Among adults who are online the rates of participation are higher: 65 percent. 

As the NYT says, "social networks have crossed another milestone." 

"It is a sign of how deeply and widely social networking companies have penetrated the lives of ordinary people and in turn, transformed the ways in which people communicate, authorities govern and companies sell things."