Thanks for your report. It's desired feature that any normal users can do shutdown. I can't tell easiest way to do that. Please don't run gconf-editor as root. I hope you find solution this problem. Forums are good place to search.
** Changed in: Ubuntu Status: Unconfirmed => Rejected -- Any user can shut down https://launchpad.net/bugs/81700 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs