I use sheets as quilt backs all the time. And I mean all the time ! I have not had any problem with them at all. I posted a picture of my Waverly Sheet Quilt about a week ago and it was all sheets, front and back. I have taken several of my quilts to my long armer Marie and she has never said one word against it, I asked her after hearing negative comments on the board. I know they say the thread count is too high, but why does it work so well for me ? I would say to try it first on one sheet and see what you think. My Bernina sails right through it with no problem at all. I do use good needles and change them often.