I adore Coursera and EdX. I was a fairly early adopter of MOOCs, and over the past three years, I have collected 63 certificates (and counting) in a wide variety of topics that interest me (including personal finance).
What I have not done, however, is used MOOCs to advance or change my career. I already have undergrad and graduate degrees in my field (biotech), and while I find the online offerings to be well worth the price tag (free), they can be rather hit-or-miss, and are not quite a replacement for a brick-and-mortar education from a properly accredited institution -- or real job experience for that matter. Most of the professors are fabulous, but there are serious limits to the inter-personal interactions and evaluation methods (the quizzes/exams tend to be a joke IMO, and peer evaluations are a total load of crock -- with all due respect to
Daphne Koller, her research was conducted at an elite university and simply cannot be generalized out to the internet population). Many of the classes tend to be trivially easy/superficial, and the ones that aren't are oftentimes too difficult without proper peer/TA/professor support.
I think MOOCs are a great way to test out the waters, to gain exposure to a new field in a structured way. And if you enjoy it, then you can pursue the area more in depth. The issue is that the barriers to entry in specialized, well-paying white collar fields can be quite high, and I'm not sure if a MOOC certificate will get you in the door the same way a diploma or even a personal contact would (I know it would never fly in my field; our degree requirements are firm) -- but it might be a good way to show interest and engagement in order to differentiate yourself from other job candidates when all else are equal. It certainly doesn't hurt to try, given the low risk involved.
As for myself, I primarily use it as a method of self-enrichment and cheap entertainment. If you have any more specific questions, I'd be happy to answer them.