I'm living in HK (now)
I've lived in HK (and Bali and...) (experiential aspect)
I've lived/been living in HK for 3 years (up until and including the present, am probably still in HK, although progressive might be "reason for absence", see next example)
I've been (living) in HK (reason for absence from a place other than HK, not sure if "I" still lives in HK or not! as Shun pointed out and JTT countered

I'm studying Japanese (now)
I've studied Japanese (and Chinese and...) (experiential)
I've studied/been studying Japanese for a year (see above)
I've been studying Japanese (=up until and including now, could be a reason for "being absent/unavailable/busy", or simply an "inform")
Hmm, seems like that whole "proform" thing is a bit counterintuitive, the Present Progressive does seem to have a different functional force to the Present Progressive.

I've neglected to say anything about the "rate of change" in Seiichi's original examples (got sidetracked by Shun and JTT). Like I said on Seiichi's other thread, I don't detect much "rate" here really, there is not much to go on after all besides the bare "facts"; I simply AM (or have been) "forgetting my English", and Ken is (or ?has been - like "impersonating"?!) "resembling his father more and more" presumably as a result of having simply aged/matured enough by now (don't let the "more and more" fool you?), although I suppose you could argue that Ken's present state is the result of a gradual process of change.
