The popularity of social networking sites such as Facebook, MySpace, Twitter, LinkedIn, and Classmates.com more than quadrupled from 2005 to 2009. These sites allow users to develop profiles of their backgrounds and interests, communicate with friends and strangers, and share thoughts, photos, Internet links, music, and more. Many users say the sites are good for our society, but others contend that the dangers of social media outweigh the benefits.
Proponents of social networking sites argue that these online communities promote increased communication with friends and family, familiarize people with valuable computer skills, and allow contact with people from around the world.
Opponents argue that social networking sites expose children to predators, increase vulnerability to computer viruses, lower worker productivity, and promote narcissism and short attention spans.
SixDegrees.com, which existed from 1997 to 2001, is considered to be the first social networking site because it was the first website that allowed users to create personal profiles and link to friends. Friendster, created in 2002, popularized social networking in the US before MySpace (2003), Facebook (2004), and Twitter (2006) took over as the most widely used social networking sites.
Facebook reports approximately 90 million users in the US and 300 million active users worldwide (as of Sep. 15, 2009), MySpace reports more than 32 million US users and 130 million worldwide (as of Aug. 4, 2009), and Twitter has an estimated 54 million users worldwide (as of Oct. 13, 2009). 35% of adults and 65% of teens in America who use the Internet have profiles on social networking sites (245 KB) . 
Social networking and blogging sites accounted for 17% (about one in every six minutes) of all time spent on the Internet (180 KB)  in Aug. 2009, nearly three times as much as in 2008. The amount of time Americans spent on social networking sites increased 83% from 2008 to 2009. Users in the US spend an average of five hours and 46 minutes per month on Facebook.  Russians spend more time on social networking sites than people in any other country, an average of 6.6 hours per month compared to the worldwide average of 3.7 hours per month.
Social networking sites play a role in shaping the political landscape in an era called “Web 2.0,” defined as a second generation of the Internet characterized by the more dynamic way in which people interact online compared to when the Internet first gained popularity. Presidential candidates in the 2008 election engaged potential voters with YouTube, Facebook, MySpace, Twitter, and other social media. More than a quarter of US voters younger than age 30 (including 37% of those aged 18-24) said they obtained information about the political campaigns from social networking sites.  On Nov. 3, 2008, the day before the US presidential election, Democratic presidential candidate Barack Obama had 2,379,102 Facebook supporters while Republican candidate John McCain had 620,359. Obama had 833,161 MySpace friends and McCain had 217,811. Obama had 384% more Facebook supporters and 383% more MySpace friends than McCain. 
In May 2009, the White House announced that it was joining Twitter, Facebook, and MySpace to meet President Barack Obama’s call one week earlier “to reform our government so that it is more efficient, more transparent, and more creative.” The Office of New Media was established with the goal of promoting communication, transparency, and participation online. When it was discovered in Sep. 2009 that the White House had begun collecting and storing information about people who post videos and comments on social networking sites, some people were worried about the invasion of privacy. The White House, however, stated that it was merely complying with the Presidential Records Act, which requires the preservation of all presidential records.
The growth of social networking sites is outpacing the development of rules, laws, and unofficial etiquette regarding their use. For example, Congressman Peter Hoekstra (R-MI) sent messages via Twitter announcing his whereabouts as he traveled through war zones during a Feb. 2009 trip to Iraq, giving rise to security concerns about the use of social media to post real-time locations.  Businesses worldwide struggle with the decision of whether to allow access to social networking sites in the office for fear of lost revenue from decreased worker productivity and security breaches. The fraudulent act of attempting to acquire personal information for identity theft, called phishing, increased 240% on social networking sites from 2008 to 2009. Two-thirds of businesses fear that social networking sites endanger corporate security, and one in four users of social networking sites unwittingly exposes himself to crime by revealing personal details.
Illinois passed a law (550 KB)  in Aug. 2009 banning registered sex offenders from using social networking sites with the goal of protecting children from online predators. However, a report from the Internet Safety Technical Task Force (2.7 MB)  presented to the US State Attorneys General found that children are less vulnerable to online sexual predators than commonly thought and adults lying about their ages to initiate relationships with minors are a rare occurrence. 43% of online sexual solicitors were identified as being adolescents (under 18), 30% were adults between the ages of 18 and 21, and 9% were adults over the age of 21. The majority of predatory encounters solicited online occur via chat rooms and instant messaging, not on social networking sites.
As social networking sites become more integrated in our modern culture, some people think that the benefits outweigh any downsides, while others believe the dangers are more pressing than any upsides.