I've been driving in Japan for about a year and half now and I must say, the mirrors all over the place are a damn smart idea. At first I thought it was silly to have mirrors all over the place, at every turn or corner. But now I think it is a great idea and when I returned home for a visit to the US I can say that I kind of wished the US would adopt the idea. They are very helpful for looking around blindspots and I think they prevent many many accidents.
Just wanted to divulge my feelings about the roadway mirrors here in Japan.
On a funny note, one time I was looking in a mirror and saw an ojisan taking a piss on the side of the road. That was one time I wished the mirror wasn't available.
BB