Apparently Apple has implemented directory hard links in their hfs+
filesystem, and it is the underpinning for the new 'Time Machine' backup
in Mac OS-X leopard, where each incremental backup of an unchanged subtree
is a single directory hard link. Seems like a very reasonable usage - though
Time Machine presumably will not work on NAS boxes lacking directory
hard link support (like Linux file systems.)
[Ref:
http://www.appleinsider.com/articles/07/10/12/road_to_mac...