Loopt, an early player in location-based social networking, has become one of the first apps to take advantage of iOS’s new multitasking ability.

It’s adding a feature that has long remained elusive for location apps on the device — in the background location. Loopt users can now continuously share where they are with specific friends so they don’t have to constantly “check-in” to places. If a friend happens to be nearby,┬áthe app will send you a push notification alerting you. (They can still do check-ins for acquaintances and a broader group of friends, however.)

Loopt’s hybrid model combines the two experiences in a fairly novel way. You can share your “live location” for specific periods of time like a couple hours with friends. It’s not an entirely new idea. Another app called Glympse pioneered this kind of temporary location sharing, allowing people to share where they were in real-time for short periods of time. (A use case might be if you’re running late to a meeting and wanted people to know where you are for 15 minutes to plan around that.)

The combination of all these different styles of location-sharing will test the dominant paradigm of user experience on location-based services. Loopt was founded before Apple’s iPhone became mainstream and originally was designed around the idea that people would constantly want to share their whereabouts.

But the design of the iPhone’s operating system long prohibited this feature because it didn’t allow multitasking, or the ability to have more than one app operating at once. Apps like Foursquare and Gowalla powered ahead with a “check-in” model of location sharing, which let people share where they were with specific friends.

Now that both types of location sharing will be possible on the device, it will be interesting to see whether “check-ins” remain popular or whether shifting social norms have made more people comfortable with the idea of constantly sharing their location without the conscious act of checking in.

The new app also offers a closer Facebook integration that will let users post updates to the social network when they check in.