The default configuration in /var/pgsql/postgresql.conf says that listen_addresses defaults to localhost, but it doesn't let me connect over port 5432. Connecting (as root, using sudo) over a Unix domain socket works fine, but I need to enable network connections.
I tried uncommenting the listen_addresses = 'localhost' line (to make it explicit), and restarting the Postgres process (with sudo serveradmin stop postgres, sudo serveradmin start postgres), but that didn't help.