The Drupal 7 Social Popularity Module aggregates the popularity of a node from Twitter & Facebook.
It searches the social networks for the nodes path/alias or both and returns the number of time it is shared.
The data is exposed to views, so you can see the Facebook comment count, Facebook like/share count or how many times it's been Tweeted. We provide an overall score of all the totals added together so you can filter/sort content based on how popular it is.
A similar module has been available for Drupal 6 for a while check out SocialScore.