When designing the user-interface, it is incredibly important to keep in mind the feedback the app provides the user, as well as feedback the user provides the app. These can be thought of as past and future tense actions. For example, the app can provide the user confirmation on what they have just done, i.e. a past action. Here are some examples of how the iPhone 3 confirms the ringer has just been turned off or on.
Additionally, confirmation can be requested from the user on a future action the user has tasked the phone to perform. The app store confirms purchase by subtly prompting the user to tap the same area of the screen a second time. The photo on the left shows the purchase button has changed from a price to a "green light" as the user gives the go-ahead to continue with the action. The photo on the right, however, shows the confirmation requested to delete the photo. The prompt is in red, in essence telling the user to "stop" and think before continuing with the action.
Ultimately, providing and requesting confirmation or feedback leaves the control, the power in the user's hands.