@spivonious: My phone is mounted near the review mirror. Since it's a Nokia device, a double tap wakes it and a single swipe unlocks it. With a decent interface from there it would be a swipe or two for anything necessary. All without the need to look at the phone, even. All in all, as safe as turning up the volume on the radio. I actually do this with audible today, but I have to "prime" the phone first before I start driving. I want the phone to do this for me when it enters driving mode.
Voice control is nice, and in many cases will be even better than having to tap, tap, swipe, swipe. Of course, today you still have to reach out and activate voice. It might be smart for Cortana to enter an "always listening" state when in driving mode. Of course, some people would like always listening to be the behavior all the time, like on some Motorola Android phones. "Cortana, call my wife" without having to even take the phone out of my pocket or press any buttons on my Bluetooth radio when I'm connected. That would be nice.