I've done a clean install of RC2, and users can't access external devices.
They are prompted for the root password. in
/usr/share/PolicyKit/policy/org.freedesktop.hal.storage.policy, I have
<action id="org.freedesktop.hal.storage.mount-removable">
<description>Mount file systems from removable drives.</description>
<message>System policy prevents mounting removable media</message>
<defaults>