An update for the Mountain Lion Developer Preview has added a new feature that silences the OS's Notification Center. The "Do Not Disturb" switch sits atop the slide-out Notification Center and prevents pop-ups from being generated when activated. The feature comes as part of a larger update to the Developer Preview 3 that debuted last month, and brings the fledgling OS one step closer to a public release. It's a very simple addition, but a welcome one — and perhaps something that we'll see filter down to iOS soon.