I use a Mountain Myrricle clamped under the brake hood. I can see behind me as far as the terrain allows. The blind spot is very small, almost non-existent. I do turn my head to check it but moving my head a few inches to one side does the trick also. Heck, If i move enough, I can see the opposite side of my handlebars. My mirror is way more effective than turning my head.

Mirror position is very important. The same mirror at the end of drop bars would be too close and low. On wide straight bars, it would be too far to the side.

I once saw a car coming behind so I went on the other side of construction cones. The car swerved at the last second and barely missed the cones. As the car passed, I saw a woman with a blackberry on her knees...

It's also useful to do my make-up at stop lights. Don't wan't lipstick all over my beard.