I've been getting 47 mpg regularly on my Prius. A few months ago I cracked the driver side mirror and the plastic shell on back came off. Around the same time I got new tires but my mileage annoyingly dropped to 43 mpg. I assumed the tires made the difference and just accepted it. Last week I finally got my mirror replaced but they forgot the plastic shell on the back. Still 43mpg. A few days ago they snapped on the plastic shell and bingo! Back to 47mpg every day! The little bit of air drag created by the back of the mirror was shaving 5mpg off my mileage! I was quite surprised that such a small thing could make such a big difference.
If you have a road where this can be done safely (and the driver not ticketed) you might try cruise-controlled round trips with the mirrors out and folded back. My guess is that they should not be worth more than a half mpg, but a careful test sounds like a good idea.
I toweda trailer with my 50" rear projection TV on it from OC to Las Vegas and got 32 MPG!!!! Well that was in 110 degree heat covering 4 seperate 4000 ft climbs. But it is a really cool TV! http://www.nextag.com/Samsung-HL-R5087W-50...333/prices-html
