I posted this on somethingawful.com, but i though it was a good theory, so i'll repost it here
Cut for whiny spoiler babies! (just kidding!)
(before this musing about there being more than one group of others, and Ethan and Goodwin being special forces others, along with Sayid's woman being the lab tech at Juliette's lab)
I'm also thinking that Alex was being used by the rest of the Others to help Kate and Sawyer escape as part of some plan. The Others are too smart to let someone like Alex run around loose, because she's demonstrated that she's not loyal to the group in any way (though she clearly is loyal to Ben, but thats very likely he is her father, and there is a bond there). Juliette's offing of Pickett also might of been a calculated move, since his wife died, he's been a loose cannon, pursuing his own agenda.
Jack, Kate and Sawyer might of been brought to the Hydra simply so Jack would operate on Ben. Sawyer was there to get Kate to do what they wanted, and then kate was there so Jack would do what they wanted. Once Ben had been operated on, There was no need to keep Kate and Sawyer, so they might as well let them go. If they just killed them, The others know that eventually the Losties would come looking for them, and the Losties have shown themselves to be both resourceful and ruthless, and even though the Others would win in a out and out fight, the price they'd pay would be too high.