It uses the Intel HD 4000 integrated graphics.
Right now I'm running at 2560x1600 and "Fair" settings, getting a little less than 30FPS idle in Pandaria. I can do a little better if I scale it down, but strangely the scale down options aren't the machine's native resolutions.
Native resolutions according to Apple: 1680 by 1050, 1440 by 900, and 1024 by 640 (source: http://www.apple.com/macbook-pro/specs-retina/)
Resolutions available for WoW: http://cl.ly/image/2p2F3M3V1j2r - spoiler, there's a ton of them and they're not round numbers.
I've got a dedicated gaming machine, so I'm only looking for moderate performance, but WoW at retina resolution looks amazing, so I'd like to squeeze out as much performance as I can.
Edit: also, "Recommended" settings only give me 16FPS.