In the social age it's critical for many organisations to interact with their online community via social networks.
Drupal and social network technologies make integration easy between your Drupal website and many of the social network platforms out there.
Content Aggregation modules can pull content from many social arenas directly onto your Drupal website, automatically populating node content.
With an array of social network plugins and widgets, Drupal websites can easily display content as embedded fields using iFrames or social network APIs (e.g. Facebook's XFBML).
Pushing content out from Drupal to social networks is also possible thanks to Drupal's many social network modules.
Finally, encouraging visitors to promote your content is possible thanks to widgets such as Google's +1 and Facebook's Like button.