on the whole jacob matter, i personally believe that jack is jacob/will become jacob.
think about it, jack and everyone he is with are in the year 1977 and lock and his people are in current real time. jack has been making some serious decisions the past week or two and has really established himself as the one in charge right now, especially with the whole h-bomb thing. so locke is going to see jacob, and i think that it will be jack. maybe not tonight on the finale, but think about it. jack will have aged 30 years or so, and will look like his dad, christian, who has really been the only one their who could be jacob in the past episodes. the way he was in the cabin and telling locke what to do, etc. so locke will go meet jacob and it will be jack in the end, 30 years older and more like his dad. also, jack has always been portrayed as a jesus-type figure, the way he saves people and has had to lead his people to a better life. it will be awesome when he comes face to face with locke.
i also think the bomb is what lies in the shadow of the statue. they will come out with the bomb under/near the statue as they are underground in the temple.