EggXpert

What you will need:

A 16GB or larger storage device (anything from a flash drive to an ipod, to a external hard drive works here)

Now all you have to do is copy the wow folder over to the external device, and then remove the item once it is done copying.

Then you just go plug it into another computer or macintosh (you cannot mix and match here), and then go into the wow folder, an hit launcher.exe and you have your World of Warcraft game ready to go.

*Note: when patching, I'd highly recommend if a big patch, copy the folder back onto computer and patch then copy back to external device. this saves time and if its a smaller device such as a 16GB flash drive you may not be able to patch

This is kind of similar to what I do with my hard drive partitions.  I always install windows on its own partition, then I install all of my games on their own partition.  Then whenever I have to reinstall windows or change OS versions, I can just copy the shortcuts from the folders on the other partition and I'm ready to go again with all of my stuff.

You do have to be careful however as some games will save data to your personal windows folder instead of your game folder, so you would want to make sure and back that stuff up, but still, it does save you the time of reinstalling a bunch of games just because you want to give windows 7 a try or something.