With many thanks to Misa and others who helped out with my question about working with hierarchical data, I have now written a blog post on how I implemented the ltree module to solve my problem.
Frankly, if you work with hierarchical data, I'm not sure I could recommend it strongly enough. I should think that even experienced, advanced SQL gurus would appreciate the simplicity ltree offers, when compared to the ugly table designs and recursive queries in order to work with hierarchical structures.
I really hope this blog post will help others in the same boat.