Spoiler: Click here to viewI don't think that it's safe at all to say that Christian is actually alive. He seems to have a lot of supernatural stuff about him, and from what (little) we've seen of Locke so far, he just seems to be alive again. I mean, Christian constantly appears where he's supposed to be (in Jacob's Cabin, near the Donkey Wheel, etc.) which seem to suggest that he's not simply reborn, but that there's also something special about him. He seems to be acting a lot more like the other apparitions that we've seen around the Island (Eko's brother, for instance), appearing where it's convenient for him to do so. Maybe that's what you were getting at, I dunno, but I don't think that you can say that he's definitely alive.