~700mb during a raid here, 64bit vista. Anyway, the main dependancy for WoW is CPU, and the engine is poorly optimized to utilize dual/quad cores (no support whatsoever for quads) to their full potential.
Don't care, it went in. People were trying to figure out why they got FPS improvements on the PTR, and it was only happening in quad cores, then that was posted. After 3.1 the game also used more threads than pre 3.1.