How are instructors compensated for teaching a Massive Open Online Course (MOOC)? This question prompted me to wonder what compensation comes with teaching a MOOC. Most of these seem to be sponsored by universities, but my university doesn't offer them and neither did my PhD institution so I have no first-hand experience on the instructor-side.

Obviously, most participants do not pay for them (some do, I guess, but I have no idea how many and they're obviously paying much less than university tuition). So, it seems unlikely that teaching such courses pays for the instructors time.

Thus, I ask: does teaching these come with compensation of any kind? Salary/bonus? Teaching load reduction? Release from service? Teaching assistants for the courses? I'm interested in compensation either from one's university or from the MOOC provider (Coursera, Udacity, edX, etc.).
As @JeffE said, every department is different. There is remarkably little information available on the compensation offered to the instructors teaching the courses. A quick search revealed this article which states that this professor at Duke University doesn't receive any compensation for teaching MOOCs, including no reduction in teaching load, or any teaching assistants. See also this scathing article which states that professors teaching MOOCs are grossly underpaid--no hard numbers anywhere though.