Layer of Abstration
OK, you've got a taxonomy full of info you want a whole bunch of distributed, internal, business users to manage and a website that displays that taxonomy, but in a very particular way crafted to the needs of customers and controlled by a centralized web group because you don't want to simply display the raw taxonomy cause that sucks for navigation much of the time, and somehow you must do the taxonomy dance to tweak how the taxonomy content flows into pages.
On back end, you store all metadata in faceted taxonomies - someone else's smart decision that preceeded you - and on front end you combine some taxonomies to create a hierarchical view for browsing and within that display, content is displayed differently depending on info from other taxonomies, other values from other facets.
In order to do the taxonomy dance - massage taxonomy displays to be more navigable - you design a little two-screen interface to manage the display hierarchy (a technologist's term for it, which I like), adding/deleting display categories (which are separate from the back end categories) and mapping children to parents.
A tricky part is that a lot of distributed people will be entering content, and only a few people will be doing the taxonomy dance. So those entering content won't necessarily see the same categories that end up in the presentation, because dancing has altered it. How, you wonder, does one make this clear and comfortable for the content authors? This process of communicating with content authors using content management systems to manage a taxonomy catalog that is then displayed according to rules and an arbitrary user interface becomes a big, fat, juicy IA challenge.