I know it's mentioned alot on here, but I don't think that anyone has ever really FOCUSED on the fact that we never see Christian's body on the island. Yes, we all assume that the smoke monster can re-animate dead bodies, like it did with Yemi, but I think that it's interesting that the producers have almost forced us to assume that this is what happened with Christian's body by never showing the dead body to us on the island. I think they are setting us up for something...
To dive further into the mystery, it is important to explore the time traveling season on the island. Many viewers have asked the question why the Losties were the only ones traveling through time, and why the Others didn't seem to. Myself, as well as many others, believed that taking refuge in the temple would protect one from getting caught in the flashes. However, it appears that Jacob did not travel through time, nor did MiB. We know this because both appear at the statue in 2007 (MiB as Flocke, of course) while the others are still in 1977. It has also been confirmed that MiB and the Smoke Monster are the same "thing." If that's the case, how did we see Christian appearing to Locke in the FDW chamber in Season 5?