More on the Christian Debate.
Christian was down in the well with Locke. That was deep in the past, in the same scene where Sawyer & Co. looked up and saw the great statue.
The sequence went as follows. They're in the present/future by the dilapidated Orchid. They go to the ancient past where there is a well, and Locke goes down. They move forward in time to the distant past, where the well is closed and the Statue is up, and it is here that Locke meets Christian. Then Locke turns the wheel and they land in '77, with Locke of course leaving the island.
So if you follow that, it means that Christian's character was around in 1800, or whatever year that was, maybe 1880, who knows. The point is, is that there are 2 possibilities.
A: Christian's character flashed with the time flashing losties
or
B: Christian was actually on the island at that time, which means he's really really old, or even a Jacob/MIB like entity
Either way, it essentially means that Christian is neither Jacob nor MIB. I think it proves that Christian is himself.
For one, and this could be wrong, but I don't believe that either Jacob or MIB flashed with the losties. The Others didn't for sure.
Now, using option A, if Christian is himself and was able to flash with the losties, then he's not MIB or Jacob in the first place. On the other hand, if MIB was using Christian the whole time, then he would have only started doing so once Christian's body made it to the island, and thus using option B, he wouldn't have been using Christian's appearance when he met Locke at the bottom of the well in the 1800's.
My Prediction?
I think Christian was on the Island back then, a long long time ago. He left, for whatever reason, and knew in the end that he would have to lead Jack through the events we're witnessing. I don't know if that means he's above MIB/Jacob, like their father, or perhaps more of a servant like Richard has been.
My point here is just that Christian's appearance at the bottom of the well in the 1800's goes a long way toward determine who he is, and who he isn't. It's a pretty big detail to consider.