Comment 2 for bug 64321

It is still annoying but I have found/made a workaround. I have changed the permissions of /proc/acpi/sony/brightness with "chmod 666 /proc/acpi/sony/brightness" so that every user can change brightness. This has to be done on every start so /etc/rc.local is a good place for it. If there are security concerns a special group could be created but most times laptops are single user systems.
However, after changing the permissions brightness could be changed through user with the script /etc/acpi/sonybright.sh and the parameter "up" or "down".
E.g. I have defined an input action for key combination ctrl+alt+up or down.