This article by John Geirland in Wired magazine is a little old - but still relevant because it is about the psychology of the online experience, not the latest technological developments.

It is an interview with Mihaly Csikszentmihalyi (say "CHICK-sent-me-high-ee"), a professor at the University of Chicago. He researches "flow", a state of "intense emotional involvement" and timelessness that comes from immersive and challenging activities. If such activities are what you hope to provide flexible learners, then this article will give you something to think about.

If you are interested in following the lead to the rest of his work http://www.brainchannels.com/thinker/mihaly.html, it is not about online at all, but more about the relationship between the exercise of skill and the achievement of happiness.