There is a really good series of articles on hierarchies and usability at the SAP Design Guild site which ever developer should read:
(look in the left side menu for the hierarchy articles)
For those who don't have time to read the articles I'll just break it down to a couple simple points below.
Now, getting to my point. KDE has been growing a lot of extra IO-slaves lately, system:, media:, homes:, settings:, and there are ideas floating around for more along the lines of movies:, music: and documents:. I can't help but get the feeling that by doing this we would just be supplementing one complex hierarchy (filesystem) that people have trouble with, with lots of extra smaller hierarchies that people can go have trouble with. I don't see the gain. I fear that this is exactly the wrong direction. Fixing poor organisation by adding even more poor organisation.
Not to mention the other problems that IO-slaves have. Firstly, they are hidden to the user. The user just doesn't know they are there. Secondly, the relationship between something in media: and the unix filesystem is a complete mystery. Also, people don't "get" URIs. They're for geeks.
I think that the only real structural solution is what Apple OS X and GoboLinux have done. Drop the unix filesystem hierarchy and think up a completely new one based on the user's needs.
Failing that, all I ask is that people keep KISS in mind.