http://www.autoblog.com/2011/10/18/gm-debuts-next-step-in-vehicle-to-vehicle-communications
The system could alert the driver of stalled vehicles on the side of the road, drivers who are abruptly stopping, averse road conditions and even stop signs and stop lights before the hazards come into view.
As opposed to actually paying attention to the road ahead
The problem I see with this is that it could lull the driver into a false sense of security. Eventually, if all vehicles have it, and all mobile devices have it, it might be semi-useful, but what if the system is malfunctioning, or there’s a car ahead broken down with no power to run it?
I got more tickets when I had a radar detector than driving without one, just because I expected the device to warn me. I would expect a similar situation if drivers come to rely on these.