OnStar can already track stolen vehicles and has done this since 1996, but they are about to upgrade the service.
On model year 2009 vehicles, OnStar will offer an optional service that can slow down a stolen vehicle remotely.
The slowdown will only be activated after police in pursuit confirm that they are chasing the vehicle at which point the OnStar will "interacts with the powertrain to reduce engine power, which will [in turn] slow the vehicle down gradually."
Pretty snazzy! This is the next step toward Knight Rider.