What is the value of a Coursera certificate? I took up an introductory course to forensic science in Coursera, because it was actually the only forensics course I could find that was accessible, however I do wonder if it is worth anything in my CV, as a student it is obviously better than nothing, but is this something good enough to show? 
How does it compare to courses completed directly through MIT open courses, or those from another famous university? And if these are assets to a CV, if I go ahead to complete enough for a degree, how does it fare in comparison to the proper degree from the corresponding institution?
Value in an academic environment: zero. Everything you learn at Coursera you'd simply learn from a textbook in a few days if you needed it for your academic research or teaching.

Value to a non-academic employer: marginal, mainly as a signaling device (this person will sacrifice his spare time over a non-trivial amount of time to improve himself), but certainly lower than a certification in a field or skill directly related to your job.

Value to a prospective spouse (as suggested by earthling): depends. I'd certainly look favorably on someone who took a Coursera course instead of watching TV.

Value to yourself: again depends, but could be highest of all. I certainly know that those courses I took were mainly for my own pleasure and benefit.