+++ This bug was initially created as a clone of Bug #282612 +++ The recently-introduced nm-applet-0.7.2 ebuild doesn't apply the same policy, so users are no longer able to configure network settings (or even run nm-applet) without manually adding the policy statement.
The new nm-applet uses consolekit to handle user policy management. Could it be that consolekit is simply not enabled for your DE or user? Check that your DE supports consolekit and that consolekit is running and see if that fixes the policy issues.
Indeed, adding the 'consolekit' service to the default runlevel addressed the issue.