I think it's an SIAI meme caused by excitement about George Ainslie's work in psychology, briefly summarized here: http://en.wikipedia.org/wiki/George_Ainslie_(psychologist) . I'm not sure if Roko picked it up from there though. There is some debate over whether human discount rates are in fact generally hyperbolic, though Ainslie's book Breakdown of Will is pretty theoretically aesthetic; worth checking out in any case, both for potential insight into human psychology and firepower for practical self-enhancement plans. ETA: Apparently ciphergoth made a post about it: http://lesswrong.com/lw/6c/akrasia_hyperbolic_discounting_and_picoeconomics/