Besides the main wow folder there is only one other one that is needed and created by the install and that is the Data folder. All others are created when WoW is run if they don't exist. The data folder is also if the big mother of them all and the one likely to be accessed more often to load graphics textures, 3D infomation, new zones ... you get the idea.

What I did, following some advice in the forums, was install once to World of Warcraft (run it so it patches to the latest), then create wow1, wow2, wow3, wow4 and copy all the files, not the folders, from World of Warcraft, except for the patch files. After I created a Symbolic Links in the wow1, wow2, wow3, and wow4 folders to point to World of Warcraft\Data.

So the data really only loads once into memory, since the clones just point to the same :-)

I run a 60 FPS (main) and 30 FPS(clones) on q6600, 4 GB, 8800 GT with Vista 64 ;-)