First let me gloat. I was right on target in predicting that time travel would be the central feature of Lost’s plot over the last two seasons.
That being said, it is important not to get lost (so to speak) in trying to figure out the details of how time travel works. Lost is no more about the mechanics of time travel than Star Trek is about the mechanics of dilithium crystals. These are just plot devices that create tensions and constraints with which the characters interact.
So, now that I’ve predicted the technical theme of the plot, let me suggest what I expect the substantive theme to be going forward. It will all be about finding one’s constant, and a constant is just a metaphor for the attachments that one has in this world that give our life meaning and purpose. In some sense we are all adrift in time and space, as are the Losties, and search for people and things to which we can tether ourselves.
Daniel has Desmond as his constant. Desmond has Penny. John Locke has his compass (likely among other things). My guess is that we will learn about everyone’s search for a constant over the next two seasons. For Benjamin Linus my guess is that Annie is his constant. For Sawyer it will be Kate.
Not everyone will find their constant. Not everyone will keep theirs. In the end, the people without constants will truly be lost.
UPDATED to add a few random thoughts:
1) Never be the whiny guy on Lost, like Neal, ‘cuz the whiny guy is always toast.
2) Marvin Candle, aka Pierre Chang, has a a baby at the beginning of the episode. Perhaps they could reproduce on the island before the “incident” caused by the negatively charged exotic material. Also, perhaps Miles is the baby, who sort of resembles Pierre Chang. This would help explain his special powers and comfort with the island.
3) Dead people who visit the living always give good advice. Anna Lucia told Hurley to avoid getting arrested, but he did anyway. That was a mistake.
4) Sun was clearly manipulating Kate and probably against what Ben wants.
5) Ms. Hawking may well be Daniel’s mom.
Jay P. Greene's Blog 
Basically an ambitious version of City Slickers?
I suppose we can reduce any plot to any other plot. We could say that it is an ambitious Scooby Doo. Shaggy and Scooby need their constant — scooby snacks. Fred and Daphne need each other. And Velma needs that turtle neck.
The difference between Lost, City Slickers, and Scooby Doo has more to do with character development, writing, acting, etc…
Whiny guy Neil reminds me of the one guy who was always toast on the away missions on original trek
I said the same thing, minus the blog to prove I said it. 😛
Ben’s constant may very well be Locke. After re-watching Season 4 on DVD, I’m convinced that those two had the same mother and are thus half-brothers. I’m also convinced that Mrs. Hawking is indeed Daniel’s mother.
Could it be that with the island skipping around, certain characters have already lived through certain events? This would explain why Locke was always saying, “This wasn’t SUPPOSED to happen!” or Ben whispering, “He changed the rules,” when his daughter was killed. It would also explain Ben’s reply of “You know I can’t do that,” when Widmore asked if he was there to kill him. If Widmore has already done something in the future, then Ben could not kill him, according to Daniel’s string theory.
LOVE that show!