I would find this sort of map to be incredibly helpful coming into a conference or other meeting of people who I don't quite know yet. It would give me a feeling for both their line of interest (as represented by their presentation), and the ability to find out more about them by clicking-through.
While it is probably too much to maintain, it would be interesting to use it for a (contained) social network. A problem, of course, is that each person has multiple facets and interests, so a mono-branch tree doesn't work as easily. Debra Amidon has kept a different example at her Entovation International Knowledge Leadership Map, which is geographic and contains several hundred KM thought leaders.