I am using a Macbook Pro most of the time.  I actually like the notification features on Mountain Lion.  Shows me when people mention me on Twitter or Facebook or when I have tasks due from my producteev todo list.  However, when I am teaching I do not want the notifications to show.

Hold down the option key and click on the notifications icon in the upper right hand corner of the Mac screen. This will silence the notifications.  Repeat to turn them back on.