I think at least THAT statement is a quite well known fact. People like you and me are at least reasonably good at managing hierarchy's (I'm personally actually to unorganized for it - I create 'temp' folders everywhere in which I just dump 'temporary' files which I keep there for years. But I get the concept just fine).
But go an look at the desktop of the office workers doing your tax papers. They dump most of their files in a single folder... Lots of people do it and I think Mac OS X, with Spotlight, has already shown that search is far more usable than folders for the 'average' person. Now imagine taking that dumb full-text indexing and augmenting it with smart meta-data extracting (including the ability to grab tags from the web etc), linking files to usage paterns etc etc - and you can hopefully imagine how much easier it gets to find what you're looking for with very little effort.