I did some research and it seems the "myth" of being able to see the Great Wall from the Moon was started long before we had even started space travel, speculated on by amateur astronomers, yes, but nobody had actually been in space yet to prove it. In actuality, because the materials used give the wall a color similar to that of the surrounding landscape, the great wall is barely even visible from the Space Station in low Earth orbit.
Since this is not a political issue, this Snopes post is actually well-cited: http://www.snopes.com/science/greatwall.asp
Good digging.