Places! - The location based reminder app for iPhone and iPad
Continued use of GPS running in the background can dramatically decrease battery life.
Places is the reminder based on your location. When you take a nap on the bus, you may miss the stop. When you visit a new city and take the public transport, you may miss the right stop just because you dont understand the local language.
Set a reminder and put your iPhone in the pocket. The app will remind you when you are close to the destination.