I can't imagine I'm the only user that routinely needs to make a US map that includes a small inset of Hawaii and Alaska. Presently, I have to add a data frame, manipulate it, duplicate all the data into it... and update each of these individually with the same layers or selections when executing any anaylses and printing a layout view.
My idea would to allow a "map inset" element to be created... that simply copies an extent within the master data frame... and allows the user to zoom in or out in that inset element. The rest of the properties (TOC, layers, projection, etc) are all those on the master data frame. Anytime the active view is updated or refreshed, these "clones" are updated along with it... this eliminates the problems associated with having to have additional frames in the TOC, and updating them seperately before distributing a document from the layout view. What a great way to emphasize a smaller area amongst the larger one quite simply and easily with the same data and selections!