  The new social media sites -- blogs, wikis, Flickr and Digg, among others --
underscore the transformation of the Web to a participatory medium in which
users are actively creating, evaluating and distributing information. Digg is a
social news aggregator which allows users to submit links to, vote on and
discuss news stories. Each day Digg selects a handful of stories to feature on
its front page. Rather than rely on the opinion of a few editors, Digg
aggregates opinions of thousands of its users to decide which stories to
promote to the front page.
  Digg users can designate other users as ``friends'' and easily track friends'
activities: what new stories they submitted, commented on or read. The friends
interface acts as a \emph{social filtering} system, recommending to user
stories his or her friends liked or found interesting. By tracking the votes
received by newly submitted stories over time, we showed that social filtering
is an effective information filtering approach. Specifically, we showed that
(a) users tend to like stories submitted by friends and (b) users tend to like
stories their friends read and liked. As a byproduct of social filtering,
social networks also play a role in promoting stories to Digg's front page,
potentially leading to ``tyranny of the minority'' situation where a
disproportionate number of front page stories comes from the same small group
of interconnected users. Despite this, social filtering is a promising new
technology that can be used to personalize and tailor information to individual
users: for example, through personal front pages.
