One of the best things about being an artist is breaking rules and doing it your way. I read all the comments on the use of sheets and they are right on. When making any sewing/quilting project what is important to know characteristics of the fabric you are using and deciding if it will work the way you want. Other than that go for it. One thing that is correct is that the heavier thread count of sheets does make it harder to needle through when hand quilting so take that in to consideration other than that, if the sheet works for you then go for it, quiltzillas be darned.