PostRank claims to measure social engagement, including blog posts responding to someone else, bookmarking an article, leaving a comment on a blog, or clicking a link to read a news item.
Let's put this to bed once and for all, folks: There's no such thing as a "duplicate content penalty." At least, not in the way most people mean when they say that.
Y. Chen, F. Tsai, und K. Chan. DDDM '07: Proceedings of the 2007 international workshop on Domain driven data mining, Seite 55--60. New York, NY, USA, ACM Press, (2007)