Originally Posted by operator
At which point paranoia dictates that you're looking in the mirror more than you are looking forward.
Oh, puh-leeze...when driving your car do you spend more time looking in the mirror than looking forward?
A mirror is simply a device for enhancing "situational awareness". With it, you can easily monitor the situation behind you without having to turn around or depend on your hearing. They work just as well, if not better, on the bike as in your car.
FWIW, I've never run off the road, or into a parked car, or anything else, when taking my 0.5 second glances back in the mirror. I do, however, ride more assertively because I can monitor overtaking traffic much easier with it than without.