Just taking a glance around the forums, and I came across something about Christian Sheperd. There was a theory that he was an unembodied consciousness living on the Island...
Then that got me thinking, we've seen what happens when exposed to the super physics of the Island, e.g. Desmond's consciousness shifts through time, but not Desmond. So given that stuff like that is possible in Lost, and other crazy mysteries, I was thrown for a loop.
Imagine this, an ancient race of humans living on the Island. Jacob, Nemy, Ilana, etc... The Island at this point in time is just an Island with supernatural properties of physics, not spiritualism-- yet.
One day Nemesis took a tumble too far near one of these super physical properties, and like Desmond, became unattached. His consciousness became a free will being on the Island, able to manipulate the properties to create things like Christian, and Yemi.
Because we know the Island is sentient, somehow. Something controlled those flashes, something controls the ghosts. Something is leading our Losties to their destination... but I can't tell you if thats Nemy or not. In my opinion, it is.