The to wash or not to wash question is probably the most "controversial" question in the quilting world. Some are vehement washers, stating the colors of the fabric will run, it will shrink too much after being quilted and washed, etc. And the other camp of non-washers say there is little shrinkage or color bleeding in good quality fabric and that post-quilt washing shrinkage gives a quilt a vintage look.
probably the best advice I've heard: I you think the quilt will be used and washed often, pre-wash fabric. If it is a wall or decorative quilt, don't bother.