In our guild when we do show and tell, it always seems like a pieced back receives "extra credit." People are impressed with the creativity.
My only suggestion about pieced backs is to always be cognizant of the challenge in "lining up" the front and back layers evenly. Seams can appear wonky if the back is at a slight angle. I like to put the majority of the creative piecing in or near the center with bigger pieces around them, so if things are a little "off", it is not noticeable.
Concerning backs in general, I avoid stripes and plaids (at least on the outsides), because it is always a challenge to have things come out evenly on the edges.