Add a note pointing out that you can't log to syslog without tweaking

the syslog configuration file (at least not on most known Unixen).
I dunno why we hadn't had that info in the docs all along ...

doc/src/sgml/config.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.150 2007/10/09 18:14:01 neilc Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.151 2007/10/20 04:00:38 tgl Exp $ -->
 
 <chapter Id="runtime-config">
   <title>Server Configuration</title>
@@ -2299,6 +2299,25 @@ SELECT * FROM parent WHERE key = 2400;
         <varname>logging_collector</varname> must be enabled to generate 
         CSV-format log output.
        </para>
+
+       <note>
+        <para>
+         On most Unix systems, you will need to alter the configuration of
+         your system's <application>syslog</application> daemon in order
+         to make use of the <systemitem>syslog</systemitem> option for
+         <varname>log_destination</>.  <productname>PostgreSQL</productname>
+         can log to <application>syslog</application> facilities
+         <literal>LOCAL0</> through <literal>LOCAL7</> (see <xref
+         linkend="guc-syslog-facility">), but the default
+         <application>syslog</application> configuration on most platforms
+         will discard all such messages.  You will need to add something like
+<programlisting>
+local0.*    /var/log/postgresql
+</programlisting>
+         to the  <application>syslog</application> daemon's configuration file
+         to make it work.
+        </para>
+       </note>
       </listitem>
      </varlistentry>