Yesterday I backed into a parking spot with someone's new Acura RDX. It has a rear view camera which displays on the dash. Having gotten used to using the audio-only backup sensors on my Escape, I became quite aware of a problem with the camera when I (very slowly) backed into something. No damage, fortunately.
You can't just look only at the screen. While you're looking down at the screen, you have no idea what else is going on. At some point you have to check forward to see if you're far enough back into the slot, if you're straight, and for "front end swing". The last time I checked the screen, it showed what looked like 6 feet yet to back up, and the various lines overlaid on the screen seemed to confirm this. So I looked forward to check the other parameters. By the time I'd finished checking forward, I'd bumped something behind. Surprise. Oops.
So part of it is a matter of getting used to what the rear view actually means (and the RDX actually has three different rear views you can choose from). But it still won't protect you from front end swing problems. An audio system on the other hand, does not interfere with your visual checking.