The best line is when Sawyer suggests Locke might want to talk to his earlier self, warn him about the future and save him some pain. Locke replies that he “needed that pain” to get where he is today. I’ve reflected before that I probably wouldn’t try to change my path – not that my younger self would listen to what I have to say now. I suspect that such a conversation would go much like one of my recent attempts at conversation here. But I do like to hope that, even if a future me might not be able to change my mind right away, I would learn more from the interaction than my past self probably would have.
As for mysteries, the episode dropped an interesting clue. Daniel suggests that the reason for the nosebleeds after the time-skips has to do with length of exposure to the island. When Miles has a nosebleed, this doesn’t make sense, since he says he’s never been to the island before. Daniel replies by asking him if he is sure. Presumably we are meant to deduce that Miles is the son of Pierre Chang! If his parents were killed (during the purge?) but he was rescued and raised/adopted by others, that would explain why he has a different last name. Then again, perhaps we have simply not heard all of Chang’s last names yet.