One of the most useful new features of OS X Mountain Lion, at least for me, is the Notification Center, which provides timely Growl-like updates from Twitter, OS X, and various apps.
Sometimes the Notification Center doesn’t always display things the way you’d like, however. For instance, it tends to group items by app rather than showing the latest updates at the top of the queue. Fortunately, there’s a fix! Just head into System Preferences, and click the Notifications pain, then in the Sort Notification Center drop-down menu, select “By Time.”
That’s all there is to it – you’ll now see the most recent updates first, regardless of app!