I'm reposting a comment Gertch
made a month ago in the "Dead is Dead"
discussion thread... I'm sure it'll be of interest.
So what happens when we follow Locke through the rest of this season and next. Then in the series finale they come across a casket. And in this casket is the body of John Locke. They look up just in time to see the John Locke they have been following dissolve into a mist and float away.
What a mind game that would be.