GnomeVFS is a modular system, so writing your own GnomeVFS module is a logical way to provide a new data access method for your GNOME application. This procedure is fairly involved and does not appear in this book. However, GnomeVFS already supports so many access methods that you likely won't need to write your own.
Another topic not covered here is the GnomeVFS API for changing the MIME type database at run time. The user can override the system .mime and .keys files with the application registry (select Desktop Preferences > Advanced > File types and programs in the GNOME menu). As an application developer, you rarely need to dig around in a user's application registry.
This book also does not touch on Bonobo, including the MIME support for Bonobo components .