Neil, the problem with expanding from simple groupings (e.g., people, process, technology) to more elaborate ones is that you can continue expanding and defining forever.  For example, my recent KMWorld presentation included 80 KM specialties (see http://conferences.infotoday.com/stats/documents/default.aspx?id=7374&lnk=http%3A%2F%2Fconferences.infotoday.com%2Fdocuments%2F159%2FA105_Garfield.ppt  ), and you can make the case that it is missing many others.

People can try to use a few simple categories to group specialties, or many categories, but such efforts will always be imperfect and incomplete.  So use the ones that are meaningful to you, and others may choose to adopt or adapt your approach.