I don't think the bomb ever goes off.........I think The Island knows that the bomb shouldn't go off and the flash happened again. I also think it might be Jacob, it seems like he's their guide and he wants them to accomplish something so he's guiding them to that goal. I think he intervenes at the most drastic times, such as when Locke fell out of the window, or Sayid was about to get run over, but Nadia got hit.
I now wondering, if that temple has been there the whole time, since they first episode when they crashed. Its almost like the wall is so high, you just can't see the temple. Lot of my friends are wondering if those people are from the Black Rock.
I think it was interesting that The Man in the Black mentioned Richard looked different w/o chains. Not sure if he meant literally or theoretically, that he killed Jacob and is not under his command anymore.
Also, The Man in Black is Locke and The Smoke Monster, as I assumed at the end of last season.