Are you looking for something like this: http://kb.tableausoftware.com/articles/knowledgebase/use-ad-hoc-groups-categorize?
Perhaps it is a start of an answer to your question. I'm not quite sure what you mean by
...to allow end users to easily identify dimension attributes by appropriate subject areas but also allow them to create their own hierarchies as they see fit.
Thanks for replying. It's close but not quite...that knowledgebase article describes grouping dimension members (i.e. in an attribute like "departments" it would let you group "HR" and "Accounting" together into a group). I'm looking to group actual dimension attributes like "order date" and "shipped date" together...the columns so-to-speak without resorting to a binding structure like a hierarchy. More like a group list of similar or related attributes.