What's the safe way to save state on iPhone that Apple will not decline?

"Temporary files used by your app should only be stored in the /tmp directory; please remember to delete the files stored in this location when the user exits the app."

How do you detect when the user exits the app? I have files that are being used in the /tmp directory that need to stay there for the app session and/or until the user is done editing a file.

I save state with SharedObjects and haven't had any problems with app store rejections. So far I have been able to publish 3 apps, the most recent of which was accepted 2 weeks ago.

I've tried the shared object method and it works great and is easy to understand, so I would like to be able to use this method, but the question remains: will this method of saving be rejected on app store?

shared object like this:

function save():void {

    // Get the shared object.

    var so:SharedObject=SharedObject.getLocal("myApp");

    // Update the age variable.

    so.data["age"] = int(so.data["age"]) + 1;

    so.data["moo"]="hej"

    // And flush our changes.

    so.flush();

}