I strongly disagree. Everywhere where you have a lot of stuff to manage (photos, music, videos, documents, links) hierarchies don't work and only tags can tame

I strongly disagree. Everywhere where you have a lot of stuff to manage (photos, music, videos, documents, links) hierarchies don't work and only tags can tame all the chaos. The analogy to "path finding" doesn't hold, imho. That's not how our brains organize information! We organize memories by association and not by some hierarchical structures.