Thanks to Steph for alerting me to this little bit of Season 4 plot info from Kristin.
"Damon Lindelof tells me, "Desmond will have to deal with the aftereffects and the guilt of [Charlie's death]. He will question whether or not Charlie would have made this sacrifice, had he not told him that was what he was going to do? He will question the role he played in Charlie's death." So, it sounds like big sexy Dezzie is haunted by Charlie's passing, as many of us fans are!"