didnt see anything about it posted yet, so..
http://kotaku.com/5916052/two-controllers-does-terrible-things-to-your-wii-u-games
https://twitter.com/Nintendo/status/210042395507695616
some kotaku hating in there.Via Twitter, Nintendo president Satoru Iwata has said, "When you use two, the framerate halves to 30 frames per second."
So that means all those 60fps Wii U games Nintendo has been banging on about slow to 30fps if you fire up a second Wii U GamePad
http://kotaku.com/5916052/two-controllers-does-terrible-things-to-your-wii-u-games
https://twitter.com/Nintendo/status/210042395507695616