When you first start SequoiaView, it scans the harddrive it is installed on. You will then see the directory you have installed the program in as a "cushion treemap". Each file is displayed as a single block. The size of the block depends on the file size. The blocks on the root directory are arranged vertically, if they are in a subdirectory, they are arranged horizontally within a rectangle that represents their directory (depending, again, on the file size), if they are in another subdirectory they are arranged horizontally again and so on.
To make it easier to separate the blocks from each other, they are rendered with a light source on the top so they look like little mountains. (You can also use a non-cushion treemap in SequoiaView, but it is much less useful.)
In the program, you can easily navigate within your directory structure (using the right-click-menu or hotkeys) and open files. When you navigate to the root directory, you immediately get an overview of all files on your harddisk. As you move your mouse over the map, the filenames appear under the mouse pointer. You can immediately see which files take up how much space, and where they are located. The blocks are arranged alphabetically so you can easily find individual files. You can filter by name or date and even colorize certain filetypes on the map. Makes finding those lost porn images much easier ;-).
SequoiaView is a very powerful implementation of the treemap concept (its rendering and harddisk scanning speeds are very impressive, but unfortunately, the source code is closed). I have made some suggestions in their forum on further improving file navigation and selection.
I believe that a program like SequoiaView could make finding data and navigating directories easier than ever before -- and I am sure the concept can be improved a lot, and extended to a variety of other areas. Linux might gain a real competitive advantage by building something like this into its file managers. While the concept is unusual at first, it may make organizing and finding files easier than ever. What do you think?