What's iOS 4.0 Location Multi-tasking abilities

Apple's developer website describe 3 types of background services an app can use, music, location and VoIP.

When they describe background location services they talk about 2 types of apps: critical and non-critical apps. A GPS navigation app falls into the 'critical' category, and location based social networks like Gowalla and Loops falls into the non-critical category.

I have several questions

1. I'm building a location based social network, like Google Latitude. this kind of app fall under the 'non-critical' category. these apps are woken up by the OS whenever the phone switches cellular towers. How often is that? how accurate is that? will 100 meter change wake up the app?

2. I was wondering if there is a way for an application to wake up every 2 minutes to sample the GPS and go back t开发者_开发百科o sleep? 2.

3. I hear there are new Alerts feature that you can schedule in advance. can these alerts wake up the app, or are they only textual notification?

4. What if I register a thread as a critical-location thread, so I have full background activity and gps access. will Apple not approve my app?

Thanks!

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As far as I know:

1. That depends on the Cell Coverage in your area. Might be 100m, might be 2km.
2. As far as I know not.
3. That's only the notification (like a push notification does not wake up the app)
4. It may be approved, but users will complain about unnecessary battery draining.