Drupal allows you to create a deep hierarchy of terms associated to nodes. However, I have found no easy way to actually use this hierarchy.
For the sake of argument, let's assume I use drupal for blogging. I have laid out a taxonomy which inludes:
Web-development
.. DHTML
.. PHP
.. Flash
Blogging
.. Community
.. Drupal
Using taxonomy/or/2 I can create a 'virtual blog' just about DHTML. However, in order to get an overview of all Web-development related posts, I'ld have to use taxonomy/or/1,2,3,4. To me, it would make a lot of sense if I could instead use taxonomy/1 or something like that, using the hierarchy to include all children of the Web-development term.
Ideally I would like to use something like /topics/web-development. This would work similar to the title filter; it would try to match a single term, but if it would find more than one candidate it would display a list of topics/terms.