I run 3 windowed WoW sessions on my laptop with absolutely no problems. But I've also turned down all the graphics sliders (except the view distance one). Each one runs at about 1280x1024 and none of them are minimized. I get at least 40+ FPS in each window (although I can only see one at a time, since they all stack on each other).

Laptop has a Core 2 Duo, 2GB RAM and a 7950gtx mobile.