Ok, I've seen this week's Lost. If you haven't stop reading now and go read my story ;)
Anyway, so Ben tells Jack he feels God or fate or whatever caused a spinal surgeon to drop out of the sky two days after he was diagnosed with a spinal tumor. Ok, fine. What that tells us is that before the crash none of the Others knew a) that there was going to be a plane crash (they were all surprised to see the plane coming down in the big season-opening flashback this year) and 2) even though they seemed to have planned for some such eventuality (Ben sends Ethan, etc to infiltrate the survivors right there on the spot, they already know to prepare a "list") they don't know at that point who is going to be coming their way.
But then why does Ben ask Jack why he never noticed Juliet looks remarkably like Jack's ex-wife? If you follow what he seems to be hinting, they used an ex-wife look-alike to try and win Jack's confidence.
But...Juliet was already right there on the island when the plane crashed. And they didn't know Jack was onboard, so why would she already be there? The story Ben tells Jack doesn't make sense that that part was all planned.
I have two possible explanations - one is that Juliet is actually related to Jack's ex and they realized this at a later date (after the crash but before the abduction). The other is one I've had since last season, that there are an elaborate set of twins (or "twinners" as Stephen King might put it) among the Others and Losties. For some reason I think Libby has a twin that may just pop up since her stint in the Mental Institution doesn't seem to match up with her established back stories (not just that she was a clinical psychologist, but also set Desmond on his round the world cruise). It's also possible there are two "Juliets" - one that's sympathetic to Jack's cause that was brought here later, and the other that we saw witness the plane crash.
There's also evidence in the first few episodes this season that Juliet may not have been able to be in two places simultaneously. She may also have some history with Sawyer. More food for thought.