I almost forgot; I've been meaning to post this for a while. It seems that, in Jetpack Joyride, somewhere between 2500 and 3500m in, when not in a vehicle, missiles effectively stop being able to hit you. I think it might still be theoretically possible for them to hit you, but I've been unable to make it happen. The downside to it is that it doesn't seem possible to get a near-miss, either. In fact, that's how I first noticed it, when trying to get near misses. I'd not quite manage to get myself in the right position, and the missile appeared to go right through me.
Fun to watch.
Anyone have a more specific idea of where the cut-off is? And should this be considered a bug, or a feature?