It would be nice to be ablet to set the volume of notifications as well. Right now, if I have my volume up, then notificationas are loud and bothersome. If I turn the volume low, everything is low.
This feature request might be better placed at the phonon settings (I'm not sure).
We had such as setting in older versions, but it was broken with a Phonon update so that it had to be removed. See bug 324975.
Notification sounds are changeable in the Audio Volume page. However they are muted by default due to bug 407397. :/