Oh. My. God.
Couple things to notice here:
1) Several of the clips are of LOST events way in the past: especially the Beechcraft falling from the cliff and someone coming out of what looks like the Swan back entrance. Juliet also finds a very familiar looking Hatch buried in the ground. Are we seeing all round time travel here?
2) Jack's underground with a mining helmet
3) Hurley and Juliet have guns
4) Locke has a compass
5) Interestingly there's no sign of Desmond. Does he have to go back as well?
I can't believe we still have three more months of waiting! Argh!