(Rummage rummage rummage...):
"Early uses of the metaphor focused on the pattern's positive aspect, namely the potential for quick progress in learning ... Over time, however, the metaphor has become more commonly used to focus on the pattern's negative aspect, namely the difficulty of learning once one gets beyond the basics of a subject."
http://en.wikipedia.org/wiki/Learning_curve
"One natural interpretation of such a curve, which was the predominant early usage (according to Wikipedia) and still exists in some technical circles, is that the thing being learnt is easy — a great amount of learning happens in a small amount of time. This is the opposite of the popular usage."
http://english.stackexchange.com/questions/6209/steep-learni...
"The phrase everyone gets wrong. Outside experimental psychology, where the term originated, I have never seen a correct usage. Learning curves show performance (e.g., percent correct) as a function of amount of training (e.g., number of trials). A steep learning curve means the organization, person, or animal quickly went from low to high performance — in other words, learning was fast."
http://blog.sethroberts.net/2008/08/18/steep-learning-curve/
alt.english.usage:
"The learning curve for bridge is not steep - on the contrary. But I have seen other examples of this confusing of "steep curve" with something that is hard to learn. The association is probably that it is hard to get uphill, but the true meaning is that with a steep learning curve a given effort will take you high up the curve and thus corresponds to something that is easy."
https://groups.google.com/forum/?hl=en#!topic/alt.usage.engl...
Definition:
"a graphic representation of progress in learning measured against the time required to achieve mastery."
...
'The phrase "steep learning curve" is sometimes used incorrectly to mean "hard to learn" whereas of course it implies rapid learning.'