Here is a recently published article – by Michael Schudson and Danielle Haas, taken from the Columbia Journalism Review. It describes the findings of a report by Indiana University professors Erik Bucy and Maria Grabe; most importantly (for me anyway) that:
[w]hat seems to matter more is not what candidates say about themselves, or what they are seen doing, but the depth of reporting and commentary that journalists add to those sound and image bites. Bucy and Grabe find that journalists are increasingly brokers of meaning in political coverage—appearing twice as much as candidates, filling more than half of each news segment with context and commentary. And their interpretations, or lack of them, matter.
It would be a huge and unwarranted jump to take this argument as confirming my view that commenting on social news sites promises to be meaningful and important – but I guess we can say it certainly points to this direction.