I never considered the wash/don't wash debate when I started quilting a few years ago and so I didn't wash. I now have a nice sized stash all neatly wrapped on comic boards and displayed in a huge antique pie safe. No way I'm unwrapping all of that, washing, ironing and rewrapping. I will probably pre wash or soak reds, blues and blacks after reading this thread, though.
I will have to say that using water on something that is not necessary is something that I couldn't do. We are carefully rationing our rainwater at this time due to drought. We only have about 12,000 gallons left right now so wouldn't even consider prewashing.