chmod -x /usr/libexec/notification-daemon reboot
are there any solutions to turn off permanently all the annoying notification messages?
Partial answer: as SL uses GNOME, this tells you the
gconf keys for disabling at least the power management's notifcations. So in case these are your "annoying" ones...
Edit another part, I think you're done with notifications if you disable the Notification Area Applet, probably via some GUI panel options.