JoAnn's also has some other wide backing fabrics...great when using your 40% or 50% coupon. I just bought some to make some curtains for my daughter's new kitchen. And JoAnn's has the Kona muslin in wide widths. I was there yesterday and my store was out of the bleached (which I wanted) but had the unbleached. The lady at the checkout said her mother is an expert quilter and recently completed her a beatifully quilted wholecloth quilt using the wide Kona muslin. She said she gets it after her mother enters it in the Ohio state fair.
There was a recent (this week) thread about using sheets for quilting. There were recommendations for what types to use for backing (avoid the high thread count as too hard to quilt). Also, Klue said she uses flannel sheets as backing for utility quilts.