My theory of the Oceanic Six is basically what Hurley said. They are all dead. I believe this basically because there lives are too perfect.

Examples

• Kate gets let off the hook of the killing charges and settles down with Jack.
• Jack marries Kate and nothing really bad is happening at all.
• Sun now is able to stand up to her father and owns part of his company.
• Hurley was having a good time until he saw the numbers on the car. That was when he first realized they were dead.
• Sayid goes home and finally marries Nadia.

Also, Jack and Hurley saw two people they knew to be dead. I believe they are all going to figure out that they are dead and be like Jack at the end of Season Three and try and get back to the island. Hurley has already figured out that he's dead and is depressed. Jack just started to realize it at the end of "There's No Place Like Home: Part 1"

Feel free to comment but please don't edit this.