One of the things I love about Drupal is the taxonomy system. It's convenient and stable... except when it's not. I got 404s for the term URLs (both system and alias) and the cryptic message "Notice: Undefined index: href in menu_local_tasks() (row 1973 in path2site/includes/menu.inc).". Well, here's what worked.
I assume that if you've build a relatively large site, you've stumbled on Nodequeue by now ( summary: it allows you to create lists of arbitrarily ordered nodes ). But clients always had a thing for imagining things that are normally tricky to do, and one of them is to create a block that has arbitrarily ordered content per section of the site, usually by taxonomy term.