While using Debian squeeze, I was able to allow a user shutdown in xfce by adding users to the powerdev group (see here: xfce: Allow shutdown for non-root users).
Now, I upgraded my system to Debian wheezy, and some stuff in xfce doesn't seem to be running smoothly as it used to, most notably the shutdown process. Clicking on the logout icon will take me to the logout screen with "logout" enabled and "restart/shutdown" being greyed out.
This thread on the xfce forum seems to mention the same problem.
The same seems to be true for access to USB drives: Even though users are in the plugdev group, permission to the external volumes is denied (the do show up in thunar or whatever file managers are used, however).
This thread on lists.debian.org seems to mention the same problem.
The old version of xfce4 (with squeeze) was 4.6, the new version of xfce4 (with wheezy) is 4.8.
Have the config files changed? Does the newer version of xfce not care about the powerdev group any more? Any hints on troubleshooting/debugging?