I noticed a little lag on the tv when I played Mario U with the GamePad at E3, but it barely even affects the gameplay. Heck it's not even noticable unless you really look at it closely. All in all, the GamePad is doing a good job streaming the video.
Edit: Never mind. I slowed down my Mario u demo and it appears that the tv's and the gamepad's video stream are in-sync; no apparent lag at all. Video update soon.
Wii U Demos in *FPS* View ;)
http://www.youtube.com/user/PxDxI







