I also like the back to coordinate with the front. If I am short of coordinating fabric, will make a scrappy strip that I can use to extend the size of the back using smaller pieces or similar colors as the front. But totally random fabrics... well, it bothers me. Most of the quilts I make are small bed sized or throws and it is common to see the back and the front often at the same time. My quilt, my choice, my stash, and my fussiness about the back. I use plenty of those "what was I thinking", "ugly fabrics" and the bin of odds and ends on the quilt top as a way to keep the "collection" under control.
