In one of the season 4 promotional videos (the one that's free on iTunes), I'm pretty sure I saw Christian Shepherd. And he was sitting in Jacob's chair! This would help prove one of my theories that Christian Shepherd is Jacob (other evidence is that his coffin was empty and Jack mentioned him in the future).

It's around 1:02 in the video. Can you check this out and see if I 'm crazy or on to something? I'm wondering what you all think.