Regardless of Journaling File System used, the PostgreSQL data files should have only its metadata journaled to avoid double journaling.
Here's what Tom Lane had to say about the issue:
"Journaling metadata is good. Journaling file contents is redundant --- turn that off if you can. (Of course, if there is anything other than Postgres files on the same device, you may not want to turn off contents journalling..."
For ext3 that means mounting the /var/lib/postgres (or wherever your postgres data is stores) with the option "data=writeback".
I've only heard great things about SGI's XFS, especially its superb ACL features.
-Roberto
