Now, the real breakthru of folksonomical-based systems like del.icio.us or flickr is not the lack of structure or commitee-based design in the ontological space, but is the idea that if two people use the same term, it's more probable than they meant the same thing than they meant different things.
P. Mika. Proceedings of the 4th International Semantic Web Conference, Volume 3729 von Lecture Notes in Computer Science, Seite 522-536. Springer, (2005)