So here are a couple of my thoughts.
Dan said the bomb needed to be put in concrete. Remember a few seasons ago when Sayid was referring to all the concrete in Desmond's bunker? He said the last time he saw this much concrete it was covering up Chernobyl.
Locke and Richard talking about the compass. Remember when Richard came to visit locke's mother when he was a baby? He put out a bunch of items and locke picked out the compass.
Who's the new cute blond with the gun who seemed to know who Dan was?
How did the bomb and the military get there? Why did they leave it or can they not find the island anymore?