Apple introduced something called the "Significant location change API" with iOS 4.. And improved upon it in iOS 5. This allows your phone to monitor cell tower strength (as it already does) to determine if your location has changed dramatically, and then uses the "A" in AGPS (the assisted part) to grab the location of the new tower/wifi you're around.
The location badge in the status bar will stay on even if a App only uses the significant location change API... so it's not always a sign your battery will be killed, I use latitude constantly to track my location and it never affects my battery life dramatically.
The GPS is not activated unless the accuracy level the developer requests is really small. (most developers, including apple, won't use the gps radio at all)
Apple uses a very large area for locations in the new reminders app, so battery life isn't hurt. I've been blocks away and still had the reminder set off.
Again, battery life is not changed dramatically, I think some testing I saw a friend do with his app (that uses the api) decreased battery life by 2-3%. All the apps use the same API, so adding more location based apps doesn't change the amount of battery life used.
Apple's explanation:
"You can request events for significant location changes only. This provides a more limited set of tracking options but offers tremendous power savings and the ability to receive location updates even if your application is not running. This service is available only in iOS 4.0 and later and requires a device with a cellular radio."
http://developer.apple.com/library/ios/#documentation/CoreLocation/Reference/CLLocationManager_Class/CLLocationManager/CLLocationManager.html
The location badge in the status bar will stay on even if a App only uses the significant location change API... so it's not always a sign your battery will be killed, I use latitude constantly to track my location and it never affects my battery life dramatically.
The GPS is not activated unless the accuracy level the developer requests is really small. (most developers, including apple, won't use the gps radio at all)
Apple uses a very large area for locations in the new reminders app, so battery life isn't hurt. I've been blocks away and still had the reminder set off.
Again, battery life is not changed dramatically, I think some testing I saw a friend do with his app (that uses the api) decreased battery life by 2-3%. All the apps use the same API, so adding more location based apps doesn't change the amount of battery life used.
Apple's explanation:
"You can request events for significant location changes only. This provides a more limited set of tracking options but offers tremendous power savings and the ability to receive location updates even if your application is not running. This service is available only in iOS 4.0 and later and requires a device with a cellular radio."
http://developer.apple.com/library/ios/#documentation/CoreLocation/Reference/CLLocationManager_Class/CLLocationManager/CLLocationManager.html