The touch screen in the controllers of the Wii U look like they have the potential to add a lot of fun to games. The controller seems kind of big, but fortunately it looks as though the buttons and control stick are grouped close together on either side, easily within thumb range. Judging by the Zelda tech demo, it seems as though Nintendo is planning to use the touch screen for item management, which sounds great. If you have the ability to place items anywhere you want on the touch screen, you could customize it in a way that works best for you.
I would also like to see it used as a mini-map sometimes, or as a second camera angle. Say you're moving blocks around because you're trying to solve a puzzle to progress in a game. The touch screen could turn into a bird's-eye view of the field you're moving the blocks around on, so you can easily see where the next one goes. Or perhaps even set a camera view to look directly behind your character, where you see what's ahead of you on the TV, and what's behind you on the touch screen.
Should be interesting to see how this feature is applied in the future.