Laura Gibbs: Plagiarism means that students are not learning. If Coursera is committed to providing a good learning experience for students in the course, then it needs to intervene with a student who is plagiarizing, making sure the student understands what it means to do original work and why that is crucial to the learning experience. This, for me, is actually the most important reason that something has to be done about this - and far better, of course, if something is done proactively, rather than after a student has plagiarized. Now that Coursera knows plagiarism is a potential problem in a course with these types of writing assignments, some kind of plagiarism education needs to take place before the writing assignments begin. In our class, that plagiarism education needs to happen ASAP.
Dennis O'Connor: For anyone interested in teaching students how to recognize plagiarism, and create proper citations consider the 21cif Plagiarism Detection Kits: http://www.diigo.com/list/wiredinstructor/plagiarism_games