Wow, lots of ideas for the back. I think in the beginning, I was so relieved to get the top done, I just used plain backing to get it finished faster...no additional effort on designing the back. I would just try to find a good deal on fabric that would make a neutral but interesting print on the back. That worked out well because my quilts ended up more as fabric art that hung on a wall. I think now that I see more "back art", I would consider putting more effort on the back if I knew the quilt was going to be used on a bed or lap.
Appreciate all the ideas you guys have though.