In addition to these screenshots you can see a 1 minute video at MacBreak.

This window shows the mounted volumes. It is updated as volumes are unmounted or mounted. The window is shown on application launch as a starting point.

(click to enlarge)
The default look of Disk Inventory X after a folder is loaded. The treemap (middle view) visualized the files by their sizes (large square means large file). The color gives a hint of which kind the file is (MP3, PDF, ...) The selection is synchronized in all views, so if you select a file in the treemap you can see where it resides in the file hierarchy (left view) and of what kind it is (right view).

Inspector Window
This is the inspector window with detailed information about the selected file or folder.

Selection List
The "selection list" resides in a drawer which opens to the bottom of the main window. This list shows all files of a specific kind or all kinds (then all files are shown). The selection list can be opened by selecting a menu item or by using the kind statistic's context menu. You can search for files with an iTunes-like search feature.