Relevant: http://www.quora.com/Why-haven-t-cars-yet-solved-the-problem...

Apparently most people set up their mirrors incorrectly by overlapping view paths, when it would in fact be better if things moved between mirrors without any overlap (e.g. rear view mirror covers the back whilst the side mirrors cover blind spots - no overlap in between).

I've tried it out and it feels rather weird, but I must say I've found it quite effective. I still do head checks, but mostly just out of habit, and it's a good extra check to use just before you change lanes.