All these people who are like "Charlie could've swam out!" are totally missing the point. He died on purpose. He thought he had to die in order for Claire to be rescued and he had accepted that.
The flash-forward was incredible, once you realised what it was. My theories include:
-Ben was the body at the funeral
-Kate had to get back to Sawyer
-Jack managed to get some people rescued and off the island but not everyone and had to sacrifice something to do so. He deeply regrets this, which is why he desperately wants back, studies maps and flies on planes left and right, hoping that they'll crash.
I wouldn't be surprised at all to see the castaways get rescued next season and then bridge to that point that we saw, with the last season or two being Jack trying to get back to the island and make things right.
Interesting to note:
The plane crashed on September 22, 2004. Each season has been one month, with Naomi being killed by Locke taking place just before new year's eve. The paper that Jack was given by the stewardess in the first flash was dated April 2007.
Naomi's people are definitely the bad guys who might help Claire, Jack, Kate, etc. get home if only to get them off the island so they can take it for themselves. I wouldn't be surprised to see Ben, Locke, Richard, and maybe some others team up and try to fight them.
The big questions now are:
-Walt. Was it the Monster, Jacob, the real Walt (and what are the repercussions if that is the case?), or something different?
-Is Penny working with Dharma, the Others, the Other Others, or by herself?
-Will Desmond make it to the beach in time to walkie-talkie Jack? Will they take him seriously? Will Jack ignore him and insist they're being rescued?
-Why is Richard taking people to a temple?
-Why the fuck do we have to wait until February to find out?