Usage of Social Media

At these Web sites, individuals and groups create and exchange content and engage in person-to-person conversations. 

They appear in many forms including blogs and microblogs, forums and message boards, social networks, wikis, virtual worlds, social bookmarking, tagging and news, writing communities, digital storytelling and scrapbooking, and data, content, image and video sharing, podcast portals, and collective intelligence. 

There are lots of well-known sites such as Facebook, LinkedIn, MySpace, Twitter, YouTube, Flickr, WordPress, Blogger, Typepad, LiveJournal, Wikipedia, Wetpaint, Wikidot, Second Life, Del.icio.us, Digg, Reddit, Lulu and many others.