A recent study at Texas A & M suggests that using voice commands to dictate a text message while driving may be just as dangerous as looking at the phone to do it. There are two factors involved. First, the driver’s brain is still distracted, especially if the voice recognition software is not recognizing voice. Second, drivers sometimes have more of a false sense of security when they use voice-to-text, leading them to not be as cautious.
I’ll be curious to see how Google Glass impacts this. (Another factor then would be distracted pedestrians in crosswalks.)