I have made several quilts using fleece for backing and even put batting in the quilts on occassion too!! (It gets cold up here in northern New England.) The rules I have always used and really have not had a problem with fleece backing: 1. Spray baste. 2. Walking foot.
Fleece backing with batting makes the warmest quilts. My kids and husband love them. We all sit under them while watching TV in the winter.