Runs fine on high settings (View distance set to low) at 1024x1280 (widescreen I think). Although, I say that but most people think that if it's below 40000000000000000 FPS IT IS UNPLAYABLE OH GOD OH GOD UNPLAYABLE.
Ironforge is a bit laggy for me when it's full (I play on a populated server), some big raid groups pull me down a bit too, the rest of the time I get a decept avarage FPS and is highly playable for me.
But, ss long as you're having fun, who cares.
(I can't complain though, I went form a 1.2ghz Windows PC with 256 RAM and an awful graphics card so it was a huge upgrade for me, kind of depressing too considering even my iBook wipes the floor with my (now thrown out) old PC)
Edit - More RAM than my set up and that makes all the difference in WoW.