UFS (FreeBSD default) already what journaling offers through soft updates.
Run mount and you should see something like:
/dev/ad0s1e on /usr (ufs, local, soft-updates)
which will tell you that you have soft-updates enabled on /usr.
Soft Updates is like journaling in that it is safe, but it provides some performance improvements. The downfall is that data is sometimes not actually written to the disk for several seconds. You are guaranteed that your file systems will remain consistent.
Some good info here: http://www.freebsd.org/doc/en_US.ISO...ning-disk.html