The trick is not to have watched the Gangnam style video, which has apparently deprived the world of nearly 5 Stonehenges. On the basis that children make up a fair amount of the viewers of the video, but require longer to build installations using monoliths, I think it's a fair assumption that children could have built at least 1 of those Stonehenges.
In fact, if you add in all the time they have spent watching Eton Style, dogs doing Gangnam style and so on, plus the time spent doing their own imitations of Psy, I'm confident that there's another Empire State Building that has been lost as well. In our household alone, Psy must have deprived the world of at least a Lego model of the Burj Khalifa and a small paper-based Wikipedia of all knowledge known to small children. On the other hand. those of you who think the last thing London needs is another one-and-a-bit Olympic parks will be wishing Psy well with his next video.