Since animations are an integral part of the user experience with the new Windows 8 operating system and the Metro design language, Microsoft is offering app developers a few tips on having fast and fluid animations for their Metro apps. On top of that, Microsoft has made available an Animation Library for developers to use.
In Windows 8, a new capability called independent animation utilizes a sperate CPU thread to allow for smooth, glitch-free animations in Metro apps. These animations also utilize the GPU to improve performance and to allow for a smooth and consistent frame rate. Microsoft recommends app developers to use the Animation Library to utilize the the platform’s independent animation capabilities. Regardless if the code is in HTML or XAML, the Animation Library shows you how to use the right animations so the interface can be fast and fluid. "We are excited about the fast and fluid user experiences that independent animation enables for Windows 8 apps. We hope that you find the Animation Library and the support for custom animations that run independently of the UI thread useful when you create compelling user experiences in your Metro style apps for Windows 8," Microsoft adds.
Source : Windows 8 App Developer Blog