Well, it seems that Coursera business model is either issuing meaningful certificates, or offering other companies potential hires (the latter being what I've understood of Udacity business model). In both cases, the certificate is supposed to mean something.
I've taken several Coursera classes, but I don't mention them in my resume and I only care about the certificates as an incentive to complete the course, but from the very nature on how these classes are graded, it would be very difficult to prevent cheating (or sharing), barring having the exams taken in real-life locations (something that Udacity optionaly provides for some of its courses if I recall correctly).
I've taken several Coursera classes, but I don't mention them in my resume and I only care about the certificates as an incentive to complete the course, but from the very nature on how these classes are graded, it would be very difficult to prevent cheating (or sharing), barring having the exams taken in real-life locations (something that Udacity optionaly provides for some of its courses if I recall correctly).