I am trying to work this out in my head (that is absolutly spinning!!). Richard tells Locke that he has to die when discussing Locke going to bring the others back.
Do you think Christian already belonged to the Island and bringing his body there (unintentional as it was) is why we are seeing him "reincarnated"?

Very good thought! I like this a lot!

If so, what are the implications? Does that mean the following belong to the island and are seen because they were on the island at some point in time

1) Kate's ghost horse?
2) Mr. Ecko's brother Remy
3) Hurley's imaginary friend

I'm sure there's a list somewhere.

I am trying to work this out in my head (that is absolutly spinning!!). Richard tells Locke that he has to die when discussing Locke going to bring the others back.
Do you think Christian already belonged to the Island and bringing his body there (unintentional as it was) is why we are seeing him "reincarnated"?

I was thinking along the same lines too. We saw Christian's dead body, it was brought to the island, the body disappeared, and then Christian began appearing to various people all over the island. We've seen Locke's dead body now, it's going to be brought to the island, and I wouldn't be surprised if Locke became a Christian-like character.

If so, what are the implications? Does that mean the following belong to the island and are seen because they were on the island at some point in time

1) Kate's ghost horse?
2) Mr. Ecko's brother Remy
3) Hurley's imaginary friend

I'm sure there's a list somewhere.

I'm not sure about the horse or Dave and how they relate, but Eko did find the body of his brother, which I think is a big difference between Yemi and Christian. I think Yemi died and then his image was imitated by the smoke monster or something like that. Whereas I think Christian is different - he's appeared to people who never knew him off-island, like Michael and Locke. So I do think Christian was ressurected by the island in some way, though of course, what exactly Christian is - alive, dead, a ghost, etc. - is unclear.

Locke could become a Christian like character... like say... Jacob? ;)

It's crazy, everyone's dying to get Jack on a plane.