(Spoiler Alert!)
Another great episode, but not too much new was revealed that could not have already been guessed.
1) Jin is alive, but not having seen him die, we could have guessed that he’d be back. In addition, having him alive will make Sun’s efforts at revenge more tragic.
2) Miles has been on the island before and is probably Pierre Chang’s (Marvin Candle’s) son, who was the baby we saw with him when the record skipped in the season opener.
3) Ben was the one sending lawyers to take Aaron from Kate, probably to push her into returning with Aaron to the island to keep him.
The introduction of younger Danielle and the French scientists suggests that much of this season will be consumed with “back-filling” the plot. That is, we are going to fill in the story of how various, previously minor, characters are actually significant parts of the plot in the past. Now that we’ve seen the younger Widmore and the younger Danielle, I bet we are going to learn about how Widmore was forced from the island and why some are allied with him and some with Ben.
I’m also pretty sure that “Ellie,” the woman who held Daniel Faraday at gunpoint as he went to dismantle “Jughead,” the H-bomb, is a younger Ms. Hawking. And Ms. Hawking is Daniel Faraday’s mom. You can see the evidence for this theory here.
I think Lost will be governed by Terminator Rules, where the future cannot be changed despite efforts to do so. And with an H-bomb on the island I fear that the end is that the island is destroyed by it. People are trying to “save the island” by changing time, but it will be doomed. And we’ll have one big time loop where “Adam and Eve” (who may be Aaron and Ji Yeon, Sun and Jin’s baby) loop back to the start of the island in time from near it’s end.
I do have some questions about Jin and Danielle. Had they met in the future? If so, did Danielle remember that she had met Jin in the past? Is it possible that we aren’t playing by Terminator Rules and Jin’s encounter with Danielle in the past is something that didn’t happen previously? Has the string of time been changed?
Also, Brian has suggested a theory that the water bottle in the canoe is going to be very significant. Perhaps the people in the canoe are members of the Oceanic 6 unknowingly (?) shooting at their former fellow castaways. Or maybe they are intentionally doing so to stop them from something horrible that they are about to do. As we back-fill we are going to see these same episodes from different perspectives.
Jay P. Greene's Blog 
You’ve almost got it, Jay, but not quite.
At the start of the final season, they’ll become aware that the bomb is going to destroy the island. They’ll spend the entire season working frantically to prevent that. All their efforts will fail. They’ll realize that you can’t change fate and accept their destiny. There will be tears and hugs all around.
Then Desmond will sacrifice his life to save the island.
Remember, you read it here first.
I think you may well be spot on, Greg. We know Desmond will return to the island because he promised Penny that he would not. We also have heard that Desmond is omehow special in his ability to change time. Desmond was the one who told Charlie that he had to sacrifice himself. And Desmond was the one pushing the button to save the world. He really will have to push The Button.
Alternate ending: Desmond survives the process of saving the island, but afterward, he can never leave it and Penny can never go back to it (or vice versa).