howto: enabling journaling on softupdates

   I try to find a suitable reading/howto for how to enable softupdates
   on
   UFS2 filesystems. As I could see, SU+J is enlisted  to be enabled by
   default in 9.0-RELEASE. What is the status quo of that?
   I've several active systems running UFS2 on their system disks while
   data/home/mass storage is ZFS. Are their any issue with SU+J?
   well, the captitalized letters confused me first time, since the first
   newfs-option
   I hit was "-J", the option for enabling softupdate via GEOM gjournal.
   Is there any special preparation to bring up an existing filesystem
   securely into
   journaling? As I read the blogs and emails in the list, it should be
   as simple
   as booting into single user mode, enabling on all partitions in
   question (even / ?)
   via -j softupdate-journaling, runing a foreground fsck, reboot ...
   that's it? Or
   is there any other additional preparation like mentioned in gjournal
   (async mount)?
   Thanks for patience and repsonding,
   Oliver