After seeing too many quilts ruined by not pre-washing, I always pre-wash. I've bought a few pre-cut fabric squares, but wash them in a mesh bag and then air dry them flat on a towel or keep them in the bag and dry in the dryer for just a while to take care of shrinking them a bit. I haven't had problems so far, and I like knowing that what I'm putting into the quilt won't change later. I know everyone has their own theories, though. Enjoy your first masterpiece!