Group commit and commit delay/siblings

Manual: http://www.postgresql.org/docs/9.0/static/runtime-config-wal.html#RUNTIME-CONFIG-WAL-SETTINGS
Recent discussion:
http://www.facebook.com/notes/mysql-at-facebook/group-commit-in-postgresql/465781235932

It is my understanding that group commit in PG works without the
commit_delay or commit_siblings being enabled. For many people coming
from other databases, the existence of these GUC seems to suggest that
group commit does not work without the being enabled.

Are these setting useful, and if so how should they be tuned?
If they are generally are not useful, should these settings be removed?

--
Rob Wultsch
wultsch@gmail.com