Social Media: To be in or to be out ?

What is happening with all those online social media ? who are using what ?

It seems to me that more and more, the barriers between the different parts of our life are becoming thinner and thinner. Some people are already wired with others from every country on earth, 24/7 with Twitter. Why spending so much time to "Twitt" with perfect strangers ? Is it a sign of an inflated ego to get as many followers as possible ?

Since the "Susan Boyle"story posted on almost every body's networks, ( I tried only Linkedin, YouTube, Facebook and Twitter) I realized that the classic media have been almost replaced by individual power and all that for FREE and almost without advertising. Amazing!

I am very curious to get more data about usage of social media. I would appreciate if someone could point to me a reliable source of data giving the types of users, the types of content and the data by country.