The percentage of Americans age 12 and older who have a profile on one or more social networking sites has reached almost half (48%) of the population in 2010, double the amount from two years ago (24% in 2008), according to a new survey from Arbitron and Edison Research. The study found the use of social networking sites is not just for the young. While 78 percent of teens and 77 percent of those 18 to 24 have profile pages,