To disable all popup notifications that comes at the top right corner use following procedure:
First rename the file /usr/share/dbus-1/services/org.freedesktop.Notifications.service file.
$ sudo mv /usr/share/dbus-1/services/org.freedesktop.Notifications.service /usr/share/dbus-1/services/org.freedesktop.Notifications.service.disabled
Now kill notify-osd with following command:
$ killall notify-osd
This way is worked for me in Ubuntu 12.04 OS.
If you don’t run “killall notify-osd” it wont effect right away.
To git rid of notification right away you need to run “killall notify-osd” or reboot machine after renaming org.freedesktop.Notifications.service file.