Here's something we didn't know. The Wii U Gamepad supports 3D.
It's not the same 3D you'll be used to from playing the Nintendo 3DS, but rather the sort which requires you to use green and magenta 3D glasses.
Apparently the 3D factor can be activated at any time during gameplay by going into the options and changing the 3D settings at "Sterescopy" and, right under, "3D Strength". The stereoscopy can be changed from Off, to Inficolor, to Side By Side or Top Bottom. Also, the 3D strength can be measured from 0 to 10, depending on your visual comfort.
The first game known to support this 3D feature is Assassin's Creed III. The same game also allows you to play the entire game on the Gamepad if you wish to do so.