Do not Disturb in iOS 6 does not disturb you with vocal notifications, and won't light up the screen. Do not Disturb is ideal when a user is sleeping, or in an important place like a meeting. But what puts Do not Disturb worlds apart the old silent switch is it's privacy, and smart settings- you can choose iPhone not to disturb you, but if the caller calls more than twice, it will ring, assuming there is a serious emergency. Or you can have only your Favorites call you-you can even set a scheduled Do not Disturb (i.e. bedtime). You can set these preferences in Settings-Notifications-Do not Disturb.