I do not prewash. Cutting and piecing is so much easier with all those chemicals still there. Washing and spraying with startch or sizing is just putting chemicals back in. Silver fish love startch. I do wash all my quilts when they are completed with a Shout color catcher and never had a problem. I have quilting buddies that just freak out that I do not prewash.
I get to come home from a day of quilt shop hopping and start making my new quilt!