I suspect there are a lot of people who would like to participate in social media, but have concerns over privacy. Anonymity may be the difference for them to participate. Of course if you don't know who you are talking to, you also need to question validity, safety, security and value. On the other hand it could be fun.
On one end of the spectrum, networks like Twitter and Facebook have acted as catalysts to organizing events like the Arab Spring or the riots of London.