Apple has announced the much-rumored Find My Friends app. The app allows you to quickly see the location of friends who have opted to share their location with you. The app will offer deep levels of customization, such as letting users set a time window when they share their information. Also, at the end of the day, location sharing stops automatically and a person's location won't be shared again until they re-enable it.
As to be expected with such a service, Apple has built in a number of privacy controls and parental restrictions. Find My Friends will work through Apple's iCloud service.