You can also copy the World of Warcraft folder from any current Mac and just fire it up. By current, I mean from a Mac with the same OS version. It can be quicker than redownloading the install.
The wow application is a stand alone install. You just copy the folder over and it works as is. You can even put the WoW folder on an external drive and run it from there. That's an easy way to quickly run WoW on someone elses computer that doesn't have wow installed.
You might want to rename the WTF if you do copy it from another computer. I think that folder contains users accounts info and settings, but it doesn't matter that much. When you login, it will create your information and you cant do much with anyones info other than look at user names and realm locations. Copying someones wow folder will copy chat logs so you'll want to erase those before doing any copying.
Just to point out, there is nothing wrong with copying the files in regards to the license. Your license exists with your account and you can install wow on a 1000 computers if you like, but you still only have one login at a time per paying account.
Battlenet is pretty awesome. Once you register a game to your bnet account, it's there forever. I have WCIII, SCI, WOW, SCII, Diablo II and III. I can redownload them if I travel somewhere and I dont have to worry about losing any disks.