Pshh, I run WoW on a MacBook 13.3" :P One of the OLD ones, with the GMA 950 video card (*sigh*... why, Apple, WHY?!)
For the sake of having better frame rates, I run it at the lowest settings and THEN use LeatrixGFX to lower them further. I get good frame rates this way
Being an avid player of World of UICraft, though, having such a small screen and low graphics makes me sad =/ So... not sure how this helps you... just don't get an older model of MacBook if you intend to be an intense gamer (LOL, duh xD)