OnStar is a decent service, but I have one reservation: I just don't want any hacker anywhere in the world to disable my vehicle. This may seem like the stuff of AM talk show discussions, but it is a definite concern.
I remember in Austin a used car company that sold cars with an engine disabling device (their customer base was sub-prime clients, so to get people to pay, they installed keypads that required a new code each pay period. Once the vehicle was paid for, the keypad was removed.) A former employee hacked the car dealer's master account for the devices, and disabled all cars, in all customer hands, causing the engine to stall and not start, and the horns to honk.
No security is 100%, and it is only a matter of time before someone cracks that and wreaks havoc. I can see a hacker in another country that doesn't like the US disabling all GM vehicles in Florida during a hurricane evacuation just for kicks.