Over the years I've had many students mention how they had been practicing, or had planned on practicing (often on a pad), while at the same time watching TV or doing some other passive activity like listening to the radio or even talking on the phone. I've always felt that this is not a good idea, as it builds and reinforces a habit of distracted playing. Usually, their justification is the idea that "well, I'm just working on my hands; I don't need to be thinking about it." No, that's never the case. Practicing is something that should always be done mindfully, listening actively, with complete attention and awareness on the task at hand. The practicer always needs to focus on many things at once, such as accuracy of exercise, sound, smoothness, time (see prev. post), clarity, smoothness, flow and musicality. These elements can't be developed in a half-hearted or casual way. Mindless practicing will NEVER cultivate mindful playing. It also helps to remember that even the most dry, calisthenic exercises are probably 90% mental training. After all, your hands & feet can't do anything your brain doesn't direct them to do.
Put another way: You wouldn't want your brain surgeon to be watching "Dancing With The Stars" while removing a tumor, would you? Any skill worth pursuing, whether a life-or-death matter or not, should be approached with the same seriousness of purpose.