Coursera, a major player in the world of providing "massively open online courses" in higher education, is making its first move into the K-12 landscape through an effort to provide free training and professional development to teachers in the United States and other countries.
If you have doubts about the quality of the education that MOOCs provide you now have cause to be worried even more. According to this announcement, not only the student entering higher education have been taught through MOOCs, so have their teachers. So much for the quality of eduction.
Of course, I am exaggerating, people will come to their senses and realise kids in K-12 don't need knowledge be poured into their brains, they need a socially rich environment with a human being for a teacher and other kids in which and because of which you learn. MOOCs for continuous development of teacher are not such a bad idea. The majority of MOOCs is used by people for continuous development anyway, so why not for teacher education. Still, there is some reason to be concerned. Research (see note) has shown that it is not so much content itself that helps teachers keep up and become better, it is content put in the context of teaching their topic, it is pedagogically enriched content. So although a MOOC might be a good way to dip into something new, to be able to teach it requires more than just listening to lectures. (@pbsloep)
Note: there is a lot of literature about this. A good point of access is Van Veen, K., Zwart, R., Meirink, J., & Verloop, N. (2010). Professionele ontwikkeling van leraren; een reviewstudie naar effectieve kenmerken van professionaliseringsinterventies van leraren. (Reviewstudie in opdracht van en gesubsidieerd door NWO-PROO Grant no. 441-080353). Leiden. Even though the mean text is in Dutch and presumably lost on many, it being a review study means it contains a welter of useful references to English papers: http://tiny.cc/wqwpyw