I noticed last year when I started wearing screaming yellow neon tops that cars seem to behave more courteously. Seeing the change in driver behavior made me a true believer.
Townsfolk sometimes tell me when they see me with my bike in town, that they could see me a mile away on the road. Since then I make sure to wear neon yellow tops EVERY time I bike. I have hot weather tank tops, breezy mesh safety vests, longsleeve jerseys, windbreaker, etc. In winter I wear wool base layers under the yellow.
I love seeing in my rear view mirror that a car far behind me is already starting to move over to give me safety room long before they reach me.