A short tutorial like this cannot possibly cover everything. Luckily, there is a lot more information out there. Here is a list of links that you might find useful (if you have any links that should appear here as well, please send them to tim at centricular dot net).
gtk-app-devel mailing list archives - search them!
gtk-demo - part of the Gtk+ source code (look in gtk+-2.x.y/demos/gtk-demo), especially list_store.c, tree_store.c, and stock_browser.c
Some slides from Owen Taylor's GUADEC 2003 tutorial (postscript, pdf, see pages 13-15)
Existing applications - yes, they exist, and you can look at their source code. SourceForge's WebCVS browse feature is quite useful, and the same goes for GNOME as well.
If your intention is to display external data (from a database, or in XML form) as a list or tree or table, you might also be interested GnomeDB, especially libgda and libgnomedb (e.g. the GnomeDBGrid widget). See also this PDF presentation (page 24ff).
your link here!