Definately wait until it's quilted and bound, then wash it. Then check it over carefully. :)
I just did a quilt for my son and his fiance and glad that I went over it carefully before giving it. After washing it (and the shrinking because I used jelly rolls and didn't pre-wash), I found a couple of places where the stitching didn't catch the binding on the back side. I just sewed those places over again.
I also used two color catchers because it was black, white and red.