I have to agree; ICN I usually wait between 2 -10 minutes, one occasion it was quite bad with a wait of about 15 mins right when I didn't need it. Normally though getting through fast requires watching which line is about to change from "Koreans" to "Foreigners" and moving across before the crowd and sometimes it's as simple as walking to the half-empty line instead of the line twice the length (I don't get why people don't do the same?!)
I do find I can be through immigration, make a call from the free telephone in the baggage hall, pay a quick visit to the loo and then find my bags are just arriving in a very slick manner.
The immigration staff at ICN did used to be friendlier than now. I get the impression they have to work longer shifts these days and are more tired/less smiley.
SIN is usually 5 mins, the maximum ever about 12 mins.
HKG 15-20 minutes (that really was long).
PEK from 1 minute but usually around 15 - 20 mins
PVG 20 mins
I usually do get off the aircraft near the front though, overtake the people who walk slowly and get to immigration before the rest of my flight.
KIX is bad for this though because you have to wait for a transfer train which creates bunching.
NGO on the other hand I find usually has no queuing.