I have a rule: if it's going in a wall-hanging, I don't need to pre-wash; if it's going in a quilt, it definitely does need to be pre-washed. We had this discussion on the "Quilt Show" web site, and everyone had a different opinion except Alex and Ricky who had the same rule. I think it's best to pre-wash: you get rid of all the "sizing" that is put in it to make it feel good to us quilters and if it's going to bleed, it will in the wash. Also, I don't put it in the washer unless it is more than 4 yards. I hand-wash it in 1 yard segments. That way, I can see if it going to bleed. If it does, I wash it several times, then treat it with a 1/4 vinegar and 3/4 water cold rinse. I've been told that this "sets" the fabric and helps to keep it from bleeding in the future. Hope this helps.
Myra