Always provide feedback for a user's actions. Visual, and sometimes audio, cues should be presented with every user interaction to confirm that the software is responding to the user's input and to communicate details that distinguish the nature of the action.
Effective feedback is timely, and is presented as close to the point of the user's interaction as possible. Even when the computer is processing a particular task, provide the user with information regarding the state of the process and how to cancel that process if that is an option. Nothing is more disconcerting than a "dead" screen that is unresponsive to input. A typical user will tolerate only a few seconds of an unresponsive interface.
It is equally important that the type of feedback you use be appropriate to the task. Pointer changes or a status bar message can communicate simple information; more complex feedback may require the display of a message box.
For information about applying the principle of visual and audio feedback, see Chapter 13, "Visual Design," and Chapter 14, "Special Design Considerations."