Since I work mainly from scraps, I don't prewash. Most of our quilts were sold over the years and our name is on each one. And it's a very unusual name, too - any one with that name is a relative. So if someone had a problem, they could find us to complain, but no one ever did. I often wonder where all those quilts are and how they are doing. I was at a rummage sale in the next town on Thursday and recognized a couple of potholders I had made!!.
The one big problem I have nightmares about but never happened, is finding out after quilting that the backing is wrong side out.