Spend a little more time getting familiar with the settings of the phone. It has a little learning curve to it, no doubt.
There is a "silence" mode that will turn the volume off for all but alerts and alarms.
There are several different audio settings that you can control independently (All found under "Settings: Sound and Display":
Ringer: There is a separate control for incoming call volume and notification (i.e. ringer) volume.
System: Haptic feedback and notification levels when touching the screen/system powers on/off, etc.
Notification & Phone Ringtones: The ringtones for the phone and SMS/Email.
Media Volume: Music/Video Volume
Those are the "stock" controllers. You can DL apps from the market that will allow you to further customize notifications.
You can also download Settings apps that will run schedules for you. Silencr Pro and Tasker are two very good apps that allow you to customize settings. Silencr is more basic, it allows you to set a schedule based on day & time for your different notification settings. Tasker is limited only by your imagination, but the UI takes a little getting used to.