Hierarchy as a form of content organization is dying. A major milestone — I want to say tombstone — in its demise is the shutdown of the Yahoo directory, which will occur at the end of the year according to an article in Ars Technica, Yahoo killing off Yahoo after 20 years of hierarchical organization. (Actually it seems to be offline already.)
As the article observes, a hierarchical directory made some sense when Yahoo was created:
In the early days of the Web, these categorized, human-curated Web listings were all the rage. Search engines existed, but rapidly became notorious for their poor result quality. On a Web that was substantially smaller than the one we enjoy today, directories were a useful alternative way of finding sites of interest.