In Drupal 6, is there an easy way to add fields to taxonomy terms where I can use them as flags in Views? Like a 'Hidden' field on a term, so that it is filtered out of a view presentation?
There is a module for Drupal 6 called Term Fields:
Term Fields allows you to define fields for taxonomy terms in the same way that CCK allows you to define fields for nodes.
The project page also claims views integration. I have only done initial testing with this, but it looks promising and is still being actively worked on.