the stories and issues that gain traction in social media differ substantially from those that lead in the mainstream press. But they also differ greatly from each other. Of the 29 weeks that we tracked on all three social platforms, blogs, Twitter and YouTube shared the same top story just once. That was the week of June 15-19, when the protests that followed the Iranian elections led on all three.
Each social media platform also seems to have its own personality and function. In the year studied, bloggers gravitated toward stories that elicited emotion, concerned individual or group rights or triggered ideological passion. Often these were stories that people could personalize and then share in the social forum — at times in highly partisan language. And unlike in some other types of media, the partisanship here does not lean strongly to one side or the other.
via pewresearch.org