I have yet to do a pieced back, but the more I see the more I like them. So much effort goes into the front, a plain back is a bit of a cop out really.
Having said that, one of my favourite quilts I've done is a throw for the couch and it's backed with a single piece of lime green faux fur. The kids love it, they love the texture, and it's definitely the all round favourite in this house.