I think the prewash question will go down in history next to how should the toilet paper hang off of the roll. But me personally, I'm just thrilled if my husband not only gets out a new roll but actually puts is on the holder. Little things in life thrill me.
I personally don't prewash. I use the excuse that I like my quilts to have the old comfy look to them. But I think it's more out of lazyness. I will say, that if I get fabic second hand I have to wash it as soon as I get it home. Just some freak thing in me makes me do that. Also, something I learned years ago from my mom: always wash a quilt or clothing you've made BEFORE giving it as a gift!!
She made a beautiful teddy bear quilt for my cousin's baby, when she washed it before wrapping it. All the fabic fell apart. Every seam held, but the fabric just went kaput on her. We would rather have it die on us and have a chance to fix it, than to have a loved one we give it to face that. Also, I have cats and Mom smokes. We do the final wash to remove any odors. My father-in-law is very allergic to our animals and I'd hate to have him not enjoy something or have a reaction to a gift at a party or dinner.
I know I'm not much of a help with the whole prewash, but I find the postwash to be invaluable!!