Entertainment Weekly article:

Snippet:
Who's in, who's out... Emilie de Ravin's maybe-dead Claire — last seen haunting Kate's dreams and hanging with Ghost Christian in Jacob's shack — rejoins the narrative in a big way after going MIA last season. A number of certifiably deceased characters will be making seemingly inexplicable return appearances this coming season, including Charlie (Dominic Monaghan, now of FlashForward), Boone (Ian Somerhalder, now of The Vampire Diaries), and birthday-ambiguous Charlotte (Rebecca Mader, who can currently be seen in The Men Who Stare At Goats). The producers also recently told my colleague Dan Snierson that Juliet is indeed toes up — but actress Elizabeth Mitchell will materialize at least twice during the final sweep of episodes. (Let's take a moment and shoot furious eye darts of blazing indignation at her new show, V, for completely letting Mitchell down with mediocre material.) Nestor Carbonell (Richard Alpert) has been promoted to series regular. Henry Ian Cusick, who plays Desmond Hume, will not be a series regular this season, but it's believed we haven't seen the last of the ex-Hatchman.


source: Entertainment Weekly