I just finished my first quilt and I used a sheet for the backing. The sweet little lady who showed me how to quilt suggested it so that's what I used. I hand quilted it and it wasn't very hard to push the needle through, but then how would I know the difference since I never quilted before?
Anyway, because it was my first, I didn't want a ton of money invested in case I didn't like it, etc. etc. But I love quilting and will probably not use sheets every time.