OR

WARNING: enabling "trust" authentication for local connections
You can change this by editing pg_hba.conf or using the -A option the
next time you run initdb.

Success. You can now start the database server using:

    /usr/local/bin/postgres -D /usr/local/var/postgres
or
    /usr/local/bin/pg_ctl -D /usr/local/var/postgres -l logfile start

Postgres Info

If this is your first install, create a database with:
    /usr/local/bin/initdb /usr/local/var/postgres

Automatically load on login with:
    launchctl load -w /usr/local/Cellar/postgresql/8.4.1/org.postgresql.postgres.plist

Or start manually with:
    /usr/local/bin/pg_ctl -D /usr/local/var/postgres -l /usr/local/var/postgres/server.log start

And stop with:
    /usr/local/bin/pg_ctl -D /usr/local/var/postgres stop -s -m fast

If you want to install the postgres gem, include ARCHFLAGS in the gem install
to avoid issues:

    env ARCHFLAGS="-arch x86_64" gem install postgres

To install gems without sudo, see the Homebrew wiki.