This was the best episode ever, period.
I thought there would be two possiblities how the the last season begins:
1) They changed the past and all of Lost never happened
2) The bomb always exploded and nothing changed
And TPTB just did both of them, thats so great!

At first i thought the alternate timeline where they didn't crash on the island will happen / begin to exist after the Losties will fulfill their quest on the "bomb-didnt-change-anything" island but because of Juliets last thoughts/words ("It worked!") I think the bomb changed everything.
The island sunk (wtf, how great was this, dharma shark!

), the plane never crashed and the Losties live their life like they do now in the flash-sidewards.
I guess somehow the alternate-losties will find out that the island exists / their live is so much miserable now than it would be on the island that the somehow manage to not light the bomb / that the crash will happen again; and after they have done that everything will happen like we see now in the present-island time, with Jacob dead and commanding behind the scenes.
I was so afraid that they would blow the last season totally, but after the first two episode I think this will be the most awesome season ever!
And we've finally got to the see the temple and some awesome chinese master-priest, woho! (+ some old faces

)
This episode answered so many questions, I guess I have to rewatch it tomorrow