If you're interested in how information diffuses through social networks like Twitter, take a look at Truthy (one of my projects):

http://truthy.indiana.edu

     Truthy is a system to analyze and visualize the
     diffusion of information on Twitter. The Truthy system
     evaluates thousands of tweets an hour to identify new
     and emerging bursts of activity around memes of various 
     flavors. The data and statistics provided by Truthy are
     designed to aid in the study of social epidemics: How do
     memes propagate through the Twittersphere? What causes a
     burst of popularity?