Back in January, 2007 I did an experiment focussing on the fuel economy effects of removing the side mirrors on my 1997 Geo Metro. Simple A-B-A-B testing was used at a speed of 70 miles per hour.
Check out the results (by the way, my car still doesn't have mirrors on it):
[YOUTUBE]http://www.youtube.com/v/Qa3Fqp1W2QA[/YOUTUBE]
Here's the kind of mirror setup I currently have on my Geo:
Feel free to discuss.