I canceled my OnStar subscription today. After very little success with using it I called them up and listened to the whole cancellation spiel. First of all they try and get you to downgrade to a cheaper package. Then when you say no they drop the price of the cheaper package.
The one thing that really annoyed me was that she said: "You do realize that when you cancel this you will lose your unlimited roadside assistance..." etc. etc. etc. Recently we had a flat tire and we called OnStar and said "we have a flat and need assistance." Their answer: "Sorry, you don't have that package." Later when I questioned that they said: "Oh, we don't know what happened but you definitely have that cover."
The directions and connections are not much good. The software that they use must be fairly simple because they can rarely find buildings around you or it takes them forever to do so.
The only reason that I would have considered keeping OnStar would have been for their automated emergency calling. If your airbags deploy then the system automatically calls OnStar and if you can't speak they will call the emergency services and send them to you. So I thought that this would be useful if I was in a remote area and drove off the road and nobody could see the car. The catch here is that when I have tried to use OnStar in remote areas there is no reception anyway and so I was unable to raise them and so this wouldn't work. In areas where there is reception there are also plenty of other motorists to call 911 if you decided to take a short cut through a river.