Lost: the big question is...?

Mo Ryan from the Chicago Tribune had a long sit-down with "Lost" showrunners Damon Lindelof and Carlton Cuse back in December, which resulted in a terrific, spoiler-free three-part interview about their approach to writing the final season, what their expectations are of the fans' expectations (and whether this could be a "Battlestar Galactica" situation, where the ending upsets some fans to a degree that they disavow the entire series as a result), what their feelings are about Ewoks, and more. It's many thousands of words, and you can read Part 1, Part 2 and, today, Part 3.

One thing that Cuselof have said, both in that interview, and at their last press tour session is that fans need to be prepared to not have every mystery explained for them. So with the final season premiere only days away (and critics aren't going to see this one in advance, since the guys don't want it getting out whether Jughead did its intended job or not), let me ask you this:

What one "Lost" mystery do you most care about getting an explanation for? And how much, if at all, will it affect your enjoyment of the final season if we get to the end and that one's not explained?

And the flip side: what one mystery would you be most surprised to get an explanation for?