To make my point clearer: what we have almost works
because errors and
omissions (plenty of which are made) are easier to find. With tags, not
I see what your point is, but there are ways to avoid your horror scenario :-)
* Watch categories/tags using the category rss feeds to monitor new additions.
* Sort category namespace pages to list new additions first
This would make them manageable even if doe to less specific tagging the
category pages would fill up with thousands of images.
An alternative would be to keep using precise categories, but take all their
toplevel categories into account when doing intersections!