A lot of people have been discussing the nature of Jacob's nemesis and his ability to control dead bodies. Considering there were two dead people brought to the island and later seen living, I think there is some distinguishing to do when it comes to who is controlling them.
1) Christian's dead body was on Flight 815. 2) Locke's dead body was on Flight 316. 3) Christian was seen walking around and living after the crash. 4) Locke was seen walking around and living after the crash.
This is where it gets tricky:
5) Christian's body was NOT found in the coffin. 6) Locke's body was shown to be inside the crate.
Therefore, I think it is very safe to say that Jacob's nemesis is NOT controlling Christian because he doesn't need their physical body in his possesion to control a dead body. Although you can argue with me that someone else could have simply taken Christian's body, I think this is very unlikely.
Please discuss and btw, this is my first post. :)