My MBP started doing that a little over a year ago ('09 MBP). I figured it's just the cooling paste getting old and useless, but never bothered to take the thing apart because I keep telling myself "I'm buying a new one next summer anyway".
I thought the retina MBPs are supposed to be quiet because of asymetric fans, so maybe that's another issue.
Well, if I just have the charger plugged in there is a slight hum of the fans with a little buzz in the right side of the keyboard. I'm guessing there is something stuck in that fan or it is off balance. When it's like this it's totally fine I can deal with the hum. But once I load even the WoW launcher its like it knows. It gets hot enough to make me jerk my hand back if I touch the top bar (above the keyboard, below the screen, where the exhaust holes are) if I hold it for 10+ seconds.
Though this could be totally normal. I have never played games on a laptop before, so im not sure what to expect. Maybe I'll pop by the apple store next time I go to the mall.
Quick edit--
I downloaded SMCfanControl to see my fan speeds and temps
Idle: Temp: 45 C
Fan Speed: 2160 rpm
Wow Open for about 15mins scanning the auction house
Temp: Spiked to 92 C for a minute then dropped to a steady 82 C after fans kicked up
End fan speed: 5930 rpm
Late edit..
I hooked up an external display and im getting the same temps but the fans aren't kicking up as high. Maybe the screen was generating a ton of heat.