On the affirmative side, closed groups for comments, questions and discussion have drawn away huge numbers of commenters from a number of sites on all spectrums. In addition, the feedback, comment structure and immediacy seem to appeal to many.
On the con side, well, who is arguing against this point? Other than the fact that Facebook is not much of a content provider. But are we seeing the difference between lectures (posts) and discussion groups (Facebook groups and discussions)?
What do you think?