Kevin - I've long admired the user interface in Hindsight Software's Meta Machine for maintaining image metadata. In particular I 'love' the way it handles hierarchical keywords via defined taxonomies (a.k.a controlled vocabularies).
This link has a .mov video ==>>
http://hsltd.us/metamachine/index.html#.
Be wary of installing the software as it comes with image library management 'baggage'. I have a suspicion Hindsight Software is 'moribund'.
BR