Social media marketing is a set of online marketing techniques that leverage social media.
In India two very active Social Media website are Facebook and Orkut.
There has been many ways in which a Drupal site can talk to Facebook and Facebook to Drupal.
Drupal for Facebook, is a set of modules that turns Drupal into a platform for developing Facebook Applications.
Try a Demo at: http://apps.facebook.com/drupalforfacebook/, http://www.drupalforfacebook.org/sponsorship
Facebook Connect provides for Facebook users to login to the Drupal site using their Facebook login.
Some other interesting references:
Drupal for facebook - Handbook page
http://www.eshilon.com/eshilon-design-blog, blog from the maintainers of facebook connect.
Drupal groups for Facebook-API