I'm super excited to see what they do with this series.
I'm calling it; a huge theme in the final year is going to be this Man of Science, Man of Faith argument that's been going on forever.
The two forces of the island, Jacob and the Man in Black, both represent a scientific issue (perhaps one of them is a Dharma Initiative experiment gone awry) and a crazy, spiritual issue. And that's the crux of season 6. Or something.
I'm going to edit this and update this with a few random theories and speculation, seeing as how I'm kinda' bored.
Ever since the time-travel aspect was made known to the show, I've said that Jack has experienced events before. Why?
In the pilot, Jack is away from the main crash site when he wakes up. He's lying on his back. Vincent gets sent over by Christian to wake him up (in a mobisode, this is cannon, btw). Jack wakes up, and boom, he's out to save the day and just be... well, Jack.
The position of him when he wakes up is really, really similar to the position that Locke and Ben both end up when they awake in the desert after turning the wheel under the island. And his position, away from the crash, can't be just written off; I think he did something off island that we haven't seen yet to relive the events of Oceanic 815 and attempt to change them for the better. He's been through this once and the outcome didn't go the way he planned.
Through course-correction, the island tries to fuck Jack's shit; he almost dies in a cave collapse, he nearly drowns, his appendix nearly bursts... but because of some variables in the show (Juliet, Charlie, etc) he survives.
Jack is different from the survivors; this much is made clear when Mr. Friendly is like "He wasn't even on Jacob's list!"
I'm calling it, Rose and Bernard were dead when they showed up in The Incident. They were Jacob and the Man in Black, respectively. Their sentiments, especially Rose's, when it comes to the antics of the survivors echoes Jacob's and MIB's conversation in the start. And I found the glance that Bernard gave Juliet when he asked if she wanted to stay for tea a bit... knowing?
And Juliet is super special. I always had this random idea of these characters being variables and constants in a giant equation; this was moreso based on the idea of how many giant events in the show wouldn't have happened if a certain character wasn't around to save the day or do something. This is just me free thinking, but Charlie saved Jack in season one and died pretty quickly after that. Eko was a driving force in the events of the second season, and he was taken care of. Hell, most of the '77 survivors should've been outta' the picture, but due to Jacob bringing back the Ajira folk, they're back in the game. I don't know, it was just more random free-thought theory than anything else. I still believe Juliet's a heavy character for the mythology.