Yes.. Go for them.. I've used shirts on a couple of quilts.. I made a rag quilt out of flannel shirts.. I bought the shirts at thrift stores during the summer, and was able to pick, and chose the quality of the flannel.. Since the shirts were used, I didn't have to worry about them shrinking, or running.. They went into the wash with hot water when I brought them home.. I now have tons of scraps, and will probably be able to make a couple of string, or crazy quilts..
Barri