I would like rsync to support the xattr "user.xdg.robots.backup" described at http://www.freedesktop.org/wiki/CommonExtendedAttributes
If rsync runs with an option --xattr-backup-flag=user.xdg.robots.backup
it should skip directories and files with that xattr set to "false".
So that a user can decide what to exclude from backup without avoid to refer directories into an exclusion file list.
I think it is also a good idea to emit a warning when such files/directories are excluded.