For example a strategy game played on a TV together with friends where each phone is not only used for controls but also showing (private) game data and more!
It has the same problem that you would encounter if you tried touch typing on an iphone keyboard. It has no physical feedback so you have no idea if you are pressing the correct button (or any button at all) on the phone screen unless you are actually looking at it. Which means you won't be able to look at the TV screen at the same time.
But there are of course ways to improve the experience.
For example, you could show the visual feedback on the TV itself, so you can see where you are touching relative to the display. Similar to how the Kinect shows where it thinks your hands are.
Personally I hate the PS3 controller as it's too small, I much prefer the xBox 360 controller and especially if it has the keyboard attached to it.
Also, on the iPhone I dislike 99% of the games that use a virtual joystick on the screen, I just can't get on with them.
But for touch interface games, what the parent post says is a joy I look forward to experiencing: A game with discreet information on the hand-held device.
A touch screen certainly isn't for 60fps twitch-gaming in my opinion.
Isn't that the whole idea behind the WiiU?