We use sheets all the time for our Guild's Community Quilts and they are absolutely fine for machine quilting. Our LQS has a mid arm machine set-up and we quilt 3 or 4 there every month. We also ignore the quilt police and trim the backing to 1 1/4" after quilting and turn it to the front and top stitch it for binding. This works well for us and produces a hard wearing quilt that is able to withstand frequent washings at some of the shelters where our quilts are donated. I often use these methods on kid quilts and college bound quilts and sheets work out very well.