I have 7 seperate wow folders on my computer
one is my main and original in prog files\blah blah. another is in the same folder that I used for my second account (ive had two accounts for quite a while) which hold my respective stuff with those characters. I then have 5 more copies of the wow folder that are exclusively for when I 5box allowing me to make settings and changes on each one without messing up my mains. This is a big thing because you will be doing some crazy keybindings and stuff to make your characters work together that you wouldnt want reflected in your solo play. I have the last 5 folders on a seperate physical hard drive to improve performance and I have a 3rd hard drive I use for fraps and it works great. One tip to save space. dont copy the patch and update files in the wow directory around. they are not used once they are installed (the files called wow-update-######.exe and wow-patch-######.exe etc) Same thing goes for when there is an update. log in with one copy of WoW and let it download the update, once it is done copy the update and patch file to each other folder and launch wow. No wasted time for downloads; I think there is a script someone wrote in the software section to do this automatically with a batch file.