My iphone 4s gave me a black screen of death after using Maps yesterday 02/18/2012. I had to wait for the battery to drain out then was able to turn it back on 12 hour later with the USB power supply.
While traveling on the highway, I used Maps to locate my current location then I pressed the on/off button to put iphone 4s to standby. After 1 hour, I could not turn it on. Pressed both on/off and the home button, the iphone 4s was unresponsive. Plugged it in the USB power supply and this did not help, the iphone 4s still gave me the black screen of death. The iphone 4s outter casing was warmer than normal so I suspected that it was still running. Let the battery drained overnite, plugged to the USB power supply and I was able to get it back on running normally again.