Views: How can I show a list of users who have a taxonomy term attached via a term reference field?
I ended up implementing this by overriding the taxonomy page with panels instead of views.  I then made the old view taxonomy term override into a content pane.  Then, to get the "User: has taxonomy term" effect, I made a view (content pane) for each vocabulary with a "Term ID" contextual filter (supplied as a panel argument) and a relationship of "Taxonomy term: User using MY TERM".  I then added these views as content panes to the taxonomy override in panels.

I had to do this for each vocabulary, but it works.