All of these issues are sensitively canvassed in this document but without specific reference to MOOCs (given the 2012 date): http://aoir.org/reports/ethics2.pdf

What interests me in relation to MOOCs is whether they are like closed LMS discussions that are covered by the kind of IRB sensitivity that regulates use of student data; or whether they are like forums on the open internet, towards which institutions have less of a duty of care. I like the AOIR approach for its willingness to entertain the significant complexity in this issue.

No simple answers, but as a qualitative humanities researcher who uses the Australian equivalent of IRB regularly in low-risk research topics, I have always taken the approach that to seek consent isn’t a burden on me, it’s a simple practice of courtesy, like a kind of handshake. As a blogger who quotes other bloggers, I try to do the same, although I have to say that sometimes when I’m cranky I don’t feel I do this so well.