Mactavish, I can't even BEGIN to wrap my mind around theories #2 and 3!
I'm a little miffed about the whole "Ben was healed in the Temple and only remembers certain important things like his evil father, but not the 815ers" thing the writers are apparently doing. But, I'm willing to wait and see if they will still reveal a little more about that whole deal (like what happened, what part(s) of his memory were erased, if any, what he really remembers, etc.). I know the writers don't have a lot of time left to delve too much into these, but right now it's just a bit cheesy and not very LOST like.
I think you are DEAD ON about Ben being made the "leader" of the Others only so Alpert could get Widmore kicked off the Island and to bide their time until Locke showed up. Alpert had known since 1955 that Locke was the REAL chosen one and he was trying desperately to get him to the Island, but the time was never quite right. Ben has been a thorn in the side of Richard and a constant source of trouble, but I don't think it's been because he's BAD, I think he truly DOES believe he should be the chosen one. I don't think he ever thought Locke would really appear, and when he did, Ben still felt he could find a way to stay in power and PROVE he was the true chosen one. It's like Ben and Locke have traded places - Ben was confident in his place until Locke came along and made him doubt himself. Locke was full of self doubt until he got to the Island and then he became confident.
I'm not sure I buy either scenario of Widmore getting Desmond to go back to the Island, but I don't have a good idea in their stead! All we know is Des ABSOLUTELY HAS TO GO BACK. And he will. That's why Ben couldn't kill him. Just as Mrs. Hawking said, the Island isn't done with him yet. (Isn't that exactly what Tom said to Michael when he tried to kill himself?)
I still think Ilana and co. are Widmore's moles and that's how he is trying to get back to the Island. That doesn't mean they aren't from ancient Island 4-toed people though. Why doesn't someone take off their dang shoes?

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And I still don't get why it was so important to show Sawyer stepping on that stick and hurting his foot a few episodes ago...
All in all, I liked this epi, but I wasn't nearly as blown away as everyone else. But that's par for the course with me! I think I'm starting to get a little frustrated with the show and how fractured it feels. But, I'm hanging in there!