I prewash everything with warm water that I doesn't get very warm. I do put in a small amount of ammonia in all my colored clothes and that should take care of any sizing that the warm water can't handle. I usually rinse the clothes/quilt material twice. I am more worried about color bleeding than material shrinkage.
If someone purchased one of my quilts I'd advise not to use hot water anyway-bright colors and all (regardless of quilt material or not) don't do well in hot water. I save my hot water (and bleach) for washing my craft and dusting rags.