Apologies for wiki article but this is about the only sort of thing I think they are acceptable for.
I'm sure you're right in that work will have been done on how many planted comments they need to start swaying people. Typing that made me think of "Nudge" by Cass Sunstein; I haven't read it, but it sounds like what I think is the general idea of that book. Think I might go and steal it
"Social Psychology: Revisiting the Classic Studies" is a good read on all of those studies (good for a layman like me that is).