Loopt has announced today that it will this week enable 'background location sharing' on its iPhone app thanks to new multi-tasking features in the Apple’s iOS 4. This means that users will be able to have Loopt running in the background and share their location with selected friends without having to specifically check in.
Loopt uses Google Maps to show you the real-time location of your friends. Loopt may also come with the option to share your location only at set times. The Loopt blog says "users choose which friends to include on the background location sharing updates, and how long to keep the location sharing turned on".
I take this to mean that Loopt will now have some form of time control. So you can select to share your location with different people only at select times of the day. For example, you could opt to share your location with your colleagues only during office hours.
The new 'background location sharing' means that Loopt can now push notifications to your iPhone when you have friends nearby, without you having to 'check-in'. It should also lead to a revolution in how location is shared in other iPhone applications.
Just wait for the thousands of companies releasing applications that will ping you when you are passing one of their stores. You may not want them but you can bet they are coming.