here are some spoilers from spoilerfix.com

Episode 2.23: Live Together, Die Alone (2-hour season finale) (Desmond-centric)
Airdate: May 24, 2006 from 9 to 11 p.m.

• 05/17 - The cast is rehearsing a funeral on the beach. There are five graves. The two most recent are open, and contain corpses of Ana Lucia and Libby, wrapped in gray flannel. "We are going to tell you why the plane crashed," says Cuse. "We're going to explain what happens if you don't push the button. And we're going to resolve the Michael-and-Walt story." (Michael's son, Walt, was kidnapped by "the others" in last year's season finale and has been missing ever since.) Desmond, the enigmatic guy originally discovered in the hatch, also reappears, and he's not in good shape, though he gives the survivors fresh hope for escape. Just as last year's finale expanded our scope of the island's boundaries, this year's will expand its relevance. "There is something else that is reverberating on our planet that is directly linked to this island," says Monaghan. "You begin to understand that what is happening there has a significant butterfly effect in the rest of the world." One more thing: we think another character is going to die, or come close. It's just a hypothesis, based on the fact that when we asked Michelle Rodriguez (Ana Lucia) to guess which character would die after Libby, she said: "I can't do that, 'cause I know." Then she clammed up. Source: Newsweek
  
• 05/16 - In a clearing of crunchy grass, the nefarious Mr. Friendly (M.C. Gainey) twirls a bolo and barks at his fellow Others: "Don't shoot! We need him." At the beach, long-lost button pusher Desmond (Henry Ian Cusick) chugs from a bottle of booze and spills a secret. (Hint: It's sick.) Down in the hatch, Eko mops up Libby's blood and speaks of damnation. And as they load their weapons, Jack and Sawyer bond over the memory of Ana Lucia. "At least I get to kill somebody now," says Sawyer, ****ing his shotgun with an emphatic crack. [...] This time, we'll see Walt again, learn what caused Oceanic flight 815 to crash, find out what that mysterious button actually does (if anything), and more. Source: Entertainment Weekly