Comment 11 for bug 268734

Attached is a patch for /etc/acpi/powerbtn.sh.

I've already tested this (single-user only) on my machine. Of course, I wasn't able to do it without valuable help:
http://samwiseandthestereotypical.blogspot.com/2008/09/using-dbus-and-ksmserver-to-logout-and.html
http://www.g-loaded.eu/2007/11/18/problems-using-libnotify-for-user-to-user-notifications/