/usr/share/roundcube/plugins/sauserprefs/config.inc.php is in roundcube-plugins-extra 0.6-20111030.
This file is owned by root:root, with mode 0o777.
It is a symlink to /etc/roundcube/plugins/sauserprefs/config.inc.php
/etc/roundcube/plugins/sauserprefs/config.inc.php