I just had a blow out on my Volt and had a very good experience with ON star. From the time I pushed the ON star button it was about 45 minutes before the tow truck was there to pick up my car.
I thought they would just tow it to the dealer and drop it off. The ON star adviser told me that it would be stored over night and then taken to the dealer ship first thing in the morning. I am not sure the reason for that but I appreciate the concern for the car.
It was kind of funny when the driver of the tow truck asked me how to start the car. He had apparently pushed the silver button to pop the key out on the fob but then didn't know what to do with it. I just hope he get's it there all in one piece.