I had an old MBP and it played great, my current 2011 is only good for leveling and low level raids and dungeons. When I travel I tend to only focus on achievements and mount farming.
Just got it and took it for a spin. 60 fps in SW on ultra. low shadow, low liquid and good particle density. Ended up capping the fps at 30 due to heat issues, but still overall i'm very happy with the result.
I have a MacBook Pro 15" with a SSD and 8GB of memz, which runs WoW at ~50+ on high-ultra settings.
The difference between the 13" and 15" is really huge imho...