Well, after some testing, I modified the /etc/Policykit/Policykit.conf as following, and my problem is partially solved. I am happy to see that gnome cpufreq-selector works now, but still no luck with shutdown/reboot. It seems to be related to the same bug as this
https://bugs.launchpad.net/ubuntu/+s...it/+bug/250506
tail -1 syslog
==============
Feb 4 11:59:51 darkstar gnome-session[2837]: WARNING: Unable to stop system: A security policy in place prevents this sender from sending this message to this recipient, see message bus configuration file (rejected message had interface "org.freedesktop.ConsoleKit.Manager" member "Stop" error name "(unset)" destination "org.freedesktop.ConsoleKit")
cat /etc/PolicyKit/PolicyKit.conf
=================================
<?xml version="1.0" encoding="UTF-8"?> <!-- -*- XML -*- -->
<!DOCTYPE pkconfig PUBLIC "-//freedesktop//DTD PolicyKit Configuration 1.0//EN"
"http://hal.freedesktop.org/releases/PolicyKit/1.0/config.dtd">
<!--
This is the default PolicyKit.conf file for GNOME SlackBuild. Some default
settings have been configured here as example. Feel free to change them
as suits your needs.
For more information and the file format, please see the manual page
PolicyKit.conf(5) for the file format.
-->
<config version="0.1">
<!-- Users in the group "netdev" are allowed to change the network
settings through NetworkManager -->
<match action="org.freedesktop.network-manager-settings.system.modify">
<define_admin_auth group="netdev"/>
<return result="yes" />
</match>
<match user="root">
<return result="yes"/>
</match>
<match action="org.freedesktop.hal.power-management.hibernate">
<return result="yes"/>
</match>
<match action="org.freedesktop.hal.power-management.suspend">
<return result="yes"/>
</match>
<match action="org.freedesktop.hal.power-management.shutdown">
<return result="yes"/>
</match>
<match action="org.freedesktop.consolekit.system.stop">
<return result="yes"/>
</match>
<match action="org.freedesktop.consolekit.system.restart">
<return result="yes"/>
</match>
<match action="org.freedesktop.hal.power-management.reboot">
<return result="yes"/>
</match>
<match action="org.freedesktop.hal.storage.mount-removable">
<return result="yes"/>
</match>
<match action="org.freedesktop.hal.storage.mount-fixed">
<return result="yes"/>
</match>
<match action="org.freedesktop.hal.storage.eject">
<return result="yes"/>
</match>
<match action="org.freedesktop.hal.power-management.cpufreq">
<return result="yes"/>
</match>
<match action="org.gnome.cpufreqselector">
<return result="yes"/>
</match>
<match action="org.freedesktop.hal.device-access.camera">
<return result="yes"/>
</match>
<match action="org.freedesktop.hal.device-access.video4linux">
<return result="yes"/>
</match>
</config>