I might be forgetting something, but I was confused as to how/when Jack and Julia were parents to David. That really surprised me. Can anyone help explain that?
David did not exist. He only existed in Jack's flash sideways I think to represent him getting over his daddy issues. Jack was able to be the dad to his "son" that christian could never be to him.
as far as juliet is concerned I think it was just the writers way of getting her back in the mix so she could hook up with sawyer again in the afterlife.
this article helps to sum things up as best as possible.
http://www.tvsquad.com/2010/05/24/lost-finale-theories-explanations/?ncid=webmaildl2
I think one of the best things about being a fan of lost was that the viewers theories always seem to be better and more original than anything the writers could write up. It was more fun trying to figure out what was going on than actually being told by the writers what everything meant.