Overalll, people who have at least some college constitute a majority on most every social metwork, and women users generally outnumber men. The gender imbalance isn't consistent, however - 82% of Pinterest users are women, while 71% of Google+ users are men. Facebook (57%)and Twitter (59%) attract more women, and LinkedIn users seem evenly split.
The most cited uses for social media are to get in touch with friends (67%) and family (64%), or to reconnect with old friends (50%). Social media is rarely used to try to make new friends (9%), find romantic partners (5%), or to follow people they don't personally know (5% report using social media to read comments from celebrities, athletes or politicians).
- Facebook has 845 million active users, and reports averaging 200 million visits per day from mobile device. The average Facebook user has 130 'friends' and checks the site about 40 times a month
- Twitter has 127 million active users, 36% of whom Tweet daily. Twitter users are also mobile - 54% will use Twitter from mobile devices.
- One of the newer social media sites, Google+ has reported getting 90 million unique visitors to the site. Google+ seems to be a more guy-friendly site (71% of users are male), and about 44% of Google+ users are single. It's also at a stage where a lot of users are looking for friends (42%), possibly to see if there are enough on the Google+ social media system to justify it's continued use.
- Pinterest, also relatively new, has 21 million unique visitors. It's users tilt heavily female (82%), highly educated (86% have at least some college), and higher-income (56% make $50,000/yr or more).
- LinkedIn reports 150 million registered users, and is used heavily for business and professional growth. 75% of users indicate they use LinkedIn for business purposes. In addition, more than 2 million companies are on the LinkedIn social network.
- Social recommendation services are much less widely used. Reddit reports 5.5 million unique visitors. Top areas of user interest (or at least of ratings) are humor, politics, and tech. Digg reports 4.6 million unique visitors, and the top areas of interest (ratings) are search engine optimization and marketing.
Not mentioned here, but also growing, is the idea of "social TV" - that is, of using social media to share comments and informations with friends about the programs you're watching. In any case, it's pretty clear that social media has caught the attention of the American public, and primarily for the "social" aspects of the service.
Source - Social Demographics: Who's Using Today's Biggest Networks, Mashable Social Media