Do Not Disturb is one of iOS's best features (when it's working, anyway), but OS X Mountain Lion doesn't have a similar setting to disable notifications at a scheduled time. Luckily, it's easy to create your own workaround.
OS X's Notification Center does have a toggle at the top of the screen to disable notifications, but you have to enable it and disable it manually. Ben Waldie at TUAW recently came to the rescue with an ingenious AppleScript that can flip that can automatically flip that switch on a schedule. You can create the scripts yourself with his walkthrough, or just download the files from TUAW.
Once your scripts are set up, you can easily trigger them with calendar appointments. So for example, you could set a recurring calendar event to disable notifications when you're at work and need to focus. Or, you could add the trigger as an alarm to any existing calendar event, which could be handy if you have a meeting scheduled where other people might be looking at your monitor.
AppleScripting Notification Center Scheduling Do Not Disturb | TUAW via Shawn Blanc