  The social news aggregator Digg allows users to submit and moderate stories
by voting on (digging) them. As is true of most social sites, user
participation on Digg is non-uniformly distributed, with few users contributing
a disproportionate fraction of content. We studied user participation on Digg,
to see whether it is motivated by competition, fueled by user ranking, or
social factors, such as community acceptance.
  For our study we collected activity data of the top users weekly over the
course of a year. We computed the number of stories users submitted, dugg or
commented on weekly. We report a spike in user activity in September 2006,
followed by a gradual decline, which seems unaffected by the elimination of
user ranking. The spike can be explained by a controversy that broke out at the
beginning of September 2006. We believe that the lasting acrimony that this
incident has created led to a decline of top user participation on Digg.
