Or as I suggested elsewhere, maybe Jack is on to the Others scheme and he is playing Juliet. Acting a part. Which would explain why he isn't acting like himself. He is letting Juliet and Ben think they have him all figured out and fooled.... I am hoping anyway. Jack ends up saving the day at some point. Like in Indiana Jones, where he winks at short round to let him know that he isn't hypnotized anymore... Probably wishful thinking but I'd like to see his character do that.