I've been model changing for quite some time now, but from the start i always had one idea that i never got around to testing.
When you open MWS and look at the different zones that you can potentially swap in and out, you will notice there are zones labeled kalimdor and Azeroth. One hot topic for explorers is GM island which we all know is located FAR to the north west corner of kalimdor. If you swap out an instance for the Kalimdor files you will notice when you zone in you are in fact on the Kalimdor continent. Yeah, big deal...
Further exploring you will find come across the concept that some effects such as fatigue and breath loss are purely positional. By that meaning that your character only enters the state when you are at certain coordinates on the actual map. Due to the fact that you're not actually in water on the server (you're still inside what ever instance you swapped out) when you swim through the ocean you not only do not lose breath, but never hit any spots where you become fatigue. Thus you are able to swim to your heart's content as far out as you like.
I my self haven't had the time to test out what's all the way to the north west in Kalimdor, but i'd assume it's the same as on the actual map - an invisible and a gap of nothingness before you hit GM island. People have rumored to be able to pass through the invisible wall and then be flung towards GM island. Like i said, there might be nothing worth while, but it might be interesting to look into testing out some things in that area.
I think i used the ZG instance to swap for kalimdor and had no problems. It was a while back, but so i'm not exactly sure if i'm remembering correctly.