LOSTs Big 50 Mysteries

IGN has a long list of mysteries that we fans of LOST continue to wait to have resolved. The list of 50 open-ended questions is pretty comprehensive (although I think a few have been resolved, just not to the author’s standards). Which mysteries would you like answered the most?

I hope that the show producers are planning to answer at least a few of the major ones in the second half of the season? I don’t mind new mysteries being revealed, but some answers (especially to those questions left over from season 1) would be nice.