I can't seem to stay away from all this great online education, and the problem worsens as supply expands and prices fall. Back in 2008 I was paying NC State about $400 a pop for some CS courses that I took online there. Now there's Coursera, edX, Udacity, P2PU and Caltech, all free.
For some of us, it's a growing habit, as confessed in the last paragraph here. But scattered evidence so far suggests that a majority of MOOC consumers are dabblers -- a bit like president Obama, who may have done a bit of blow but didn't quite become a coke head. Below is a picture that supports this view.
The Learning From Data class at Caltech consists of 18 lectures, offered both over YouTube and iTunes U. I did both. If I knew I would be watching on a plane or in a hotel room, I downloaded them ahead of time to iTunes. Otherwise, I just watched them on YouTube. You can count the views for each video and of course they will change over time, but I think the general trend is right: a lot of people watch the first lecture, then peter out, with some peaks that may well be random, but my guess is that they are at specific topics visited by people who use this class as another reference.
My own experience may be typical. Though I took at least two online courses per year since the fall of 2008, I signed up for more. I have both signed up for courses I never took, and started courses I never finished. What can I say? It's a feast out there. I am grateful to the hosts, and I hope that they will get lots of good guests with the necessary youth and stamina. I mean, if I were an unemployed millennial, I'd occupy this.