I would not wash it. But I like the shrink that occurs after quilting - because I like that crinkly look. I allow for this when planning out my quilt. Also, I prefer handling fabric for quilting that has not been washed (though not as much of a difference when you are talking about a big backing piece).
When I wash, I always throw in 2 to 3 Color Catchers (depending on the quilt size and colors used). I have tried pre-washing and not washing. This is just the preference I have come to after trying both methods. I know that as Tallchick said, you will receive different opinions on this.