I'm a dedicated pre-washer - for many reasons, and because of that I avoid pre-cuts. I will buy fat quarters, and I will wash them, and I will cut the threads to get them apart!!
But, like Kim said above ... I will NOT pre-wash if my fabric is planned for an OBW or any other method that requires that the print be precisely measured and cut in repeats. I learned this the hard way when I purchased 4 identical panels to fracture and after pre-washing those suckers were no longer square, would not get square, and as a result I could not get a perfect match of the print from one panel to the other when you stacked them together.