This guy gets it:

When you want to eat, you go to the refrigerator. When you want to listen to music, you go to your stereo system. Completing these actions just requires knowing the locations of the things you want to use. If you want to look at photos in the real world, everything you might want to accomplish is in a single place: in the album on the bookshelf. The photos themselves are even inside the album.

Because most computer operating systems don’t organize things this way, accomplishing simple tasks can be extremely confusing for casual computer users; doing anything requires the user to know several things before he can even start his task. … With the iPhone’s interface, the user only has to know which application to open. The files are simply always available.

I wrote about this several weeks ago, though Curtis says it more succinctly and clearly than I did. And I stand by my conviction that hierarchical filesystems (i.e. paths, volumes, endlessly nestable directories) define computers as we know them, that filesystems are going away sometime soon, at least for non-power users, and then we'll see a new generation of post-filesystem user interfaces that are simpler, easier and more focused. In other words, more like "app consoles" than "computers."