So... I just had this thought.
Imagine you logged out in the barrens and when you log back in you are free falling into a canyon of lava. "Oh Sh-" Or worse... The land by the canyon is somewhat raised, right? What if you logged out at that X,Y,Z position pre-cataclysm; then when you log back in your Z is bellow the ground and you're free falling into the nothingness bellow the map.
I really don't expect this to happen to someone, unless they deliberately try it.
Just an interesting/funny thought. :]