Two player support comes at a cost.
http://www.nintendoworldreport.com/news/30489
Nintendo posted a Twitter update about playing with multiple Wii U GamePads, stating that for games that utilize two controllers will experience a drop in framerate. The Wii U will lower the framerate to at least 30fps. Apparently switching one off will smoothly transition the framerate back to normal.
Have they stated how the Gamepad connects to the WiiU, is it blutooth like wii remotes?
Will that affect online performance? I wish Nintendo included an Ethernet port (unless they did already and I didn't get the memo). I wonder why they're so against it.