k..my friend is using a different phone when the korean tech told her not to use the app killer. maybe SGS is different.
i use a SystemPanel Lte app (a kind of app killer), which show the Active and Inactive (Cached) App on the background, to check the mem usage.
it does not lag much more then if i kill all the apps, but there was one time the battery does deplete very fast..not sure if it's due to the GPS or Wifi enabled or something else.
then i kill all the apps again.
now battery is ok even when i didn't kill, as it's sort of no point killing since the random apps keep re-running themselves again in the background, after everytime u kill them all.
it's silly...hmmm...still have to experiment a while.