rdiff-backup and duplicity are very practical backup tools that use the rsync algorithm to efficiently copy over the network and, unlike normal rsync, also store historical versions. rdiff-backup uses a mirror+reverse-delta format and duplicity uses a base-version+forward-delta format. The latest version of librsync, on which both projects are based, should also transport Mac OS X metadata, so it could also be useful for OS X. I have already successfully used rdiff-backup for Linux backups.