Social Media :

Sites that is based on user participation and user-generated content are called social media . They include social networking sites like LinkedIn or Facebook, social bookmarking sites like Del.icio.us, social news sites like Digg or Sphinn, and so many other sites.

Social Media Optimisation(SMO) :

Social Media Optimisation is the process of generating traffic , brand and buzz by participating in various social media sites. Social media allows people with same interest and views to come together,participate and share their ideas and knowledge.

Social Media Sites :

Myspace is a Social Networking site with millions of users (around 189 Million) . Here links are re-directed , so no SEO value , but can acquire trafic.

Face Book got around 90 Million users . Face book allows HTML tags , but the pages are not indexed by search engines . So you can except traffic.

I will soon publish a full list of social media sites , so that you can download and use