On the other hand, if you are working full time and have a family, it is a real challenge to fit the required work in.
I have taken two courses from Coursera, Intro to Databases (8 weeks), and Algorithms part 1 (5 weeks). A shorter course is definitely more managable in terms of time-commitment.
I written about my experience in more detail here: http://henrikwarne.com/2011/12/18/introduction-to-databases-... and here http://henrikwarne.com/2012/05/08/coursera-algorithms-course...
I was somewhat surprised, though, to find that the final exam also has no time limits. I couldn't get one of the 12 exam questions right, but apparently I can come back at any time I feel like another go at turning that last question into a green tick. I'm not even sure if there's anything to stop me reading the "spoiler" forum questions about it first.
The course has been excellent and has some respected names behind it, so I had thought that the transcripts and certificates offered had some sort of credibility, but I guess I was wrong expecting my end grade to be any more credible than how many Codecademy badges I have. (Codecademy is good fun too!)
There isn't, except your own drive.
> I had thought that the transcripts and certificates offered had some sort of credibility
The certificates as they are now are more for your self as a proof of accomplishment thing. I have heard that they may be moving towards a real closed exam provided by something like Prometric, like any number of IT certifications, that would be something that could be pointed to in a more credible manner.