Writing PocketExplorer has given you a good look at the TreeView, FileSystem, and File controls and provided you with a tool not supplied with the PocketPC that you can actually use.
Of course, the File control has a lot of functionality that I didn't touch on for manipulating delimited text, binary, and random-access files, and I fully recommend exploring those functions. I commonly use the File and FileSystem controls for handling things such as configuration and .ini files for applications, but you could use them to save data or even save application state. The uses are limited only by your imagination and inclination.
You also saw examples of how to work around such problems as the CreateObject memory leak, the lack of Format() support, and the lack of user-defined properties. You even looked at making functions reusable by making them generic. These lessons can be applied to almost any eVB application, and you'll see similar code practices throughout the rest of the book.
If you want to do more exploration by extending the PocketExplorer application, the following modifications come to mind:
Add images to the TreeView for folders.
Save the state of the application so when users next launch PocketExplorer, it starts in the same folder from which they exited.
Replace the Edit, Delete, and New buttons with a MenuBar (see Chapter 4).
Add a Save As feature to frmView so users can rename the file when saving.
Allow users to rename files or folders from frmMain.
Add delimited file support (look at the InputFields and WriteFields methods).
Add a popup menu for file operations