I did a search and found lots of info on the blackbox. It looks like GM has been installing them since 1994. They were first installed in Camaros in 1996 and have been in Corvettes since 1997.
It appears that most of the boxes record the last 5 seconds of data before an air bag deployment or in some cases a near
air bag deployment. After an air bag deployment the crash data is permanently recorded on a e-prom inside the blackbox.
I've been told the box also controls your air bag system. So if you try to take it out your air bags won't work and it will set codes.
Not only do the courts use the info against you, your insurance company will use it against you too. It shows all the things they would want to know including your speed and if you were wearing your seat belt (could they try to deny medical someday for not wearing your seatbelt?). If the insurance company gains access to your car (body shop?) you can bet they will read it. Most insurance companies have the software and all they have to do is plug the box into their laptop.
The data recording was supposed to be for air bag safety research, but we can all see where it's gone now.
In the C5 the box is located...
"Behind accessory trim plate, under heater and AC control".
Here is a pic of it in a 2001 Cadillac...