The improved Notifications in OS X 10.9 are great. Not only can you respond to notifications as they appear on your desktop, but the new Notification Center also lets you know when your peripherals are about to die.
Now when your keyboard or mouse is getting low on juice, OS X Mavericks will display a notification alerting you that it’s almost time to change the batteries. The days of getting caught with a dead mouse during a presentation may finally be over.