You know the thing that drives me the most nuts about this show? When they have one of the others as a captive, why do they not grab them by the throat and scream "How the fuck do you know me!!??".
I mean Sayid(sp?) is a certified professional torturer, and the rest of the cast had little trouble with the notion of torturing Sawyer, so why don't they go to work on these people? I doubt they can all withstand it.
Even short of torturing, maybe at least open a line of dialog/questioning as to who they are, why they are there and how the hell do they know everything!