Apple has released an update to the developer preview of their next operating system, OS 10.8 Mountain Lion. The new update doesn’t appear to add much in the way of features, but it does bring the OS one step closer to its public release, which is expected sometime this summer.

Apple announced Mountain Lion rather abruptly back in February. Continuing a trend Apple began last year with OS 10.7 Lion, Mountain Lion brings several features from iOS into OS X. New features include Notes and Reminders apps, AirPlay mirroring, Game Center, OS-wide Twitter integration, iMessage, and the Notification Center.

Speaking of the Notification Center, 9to5Mac has found one new feature that’s been added to Mountain Lion in the latest developer preview. Apparently the Notification Center now has a Do Not Disturb feature:

Activated by clicking a crescent moon symbol on the menu bar, this feature suspends new notifications, allowing you to focus on whatever you’re doing without being distracted by emails, alerts, iMessages, or other notifications. It is apparently even possible to set particular times during which you don’t want to be disturbed.

While first Lion and now Mountain Lion have focused on bringing iOS features “back to the Mac,” this do not disturb toggle is not to be found in iOS. That said, it’s the kind of feature that could be extremely handy for iPhone and iPad users, so don’t be too surprised if you see it in iOS 6 later this year.

Apple has not announced a release date for Mountain Lion as yet. The original announcement said that the new OS would be coming in “late summer 2012.” It’s a fair bet that Mountain Lion, along with iOS (maybe even iOS 6?) will be a major focus of this year’s Worldwide Developers Conference, which is scheduled for June 11-15 in San Francisco.