Here is a list of items that are tested in your Windows 8 App. If you are in Southern California, please email this post for more information on getting a token for your app by June 30, 2012!

Purposeful, well-designed animations bring apps to life and make the experience feel crafted and polished. Help users understand context changes, and tie experiences together with visual transitions. If you want to have a fast and fluid application, look into the guidelines for drag and drop, edge-based animations, transitions, and UI animations.
Don’t forget to follow Metro design principles. If you want to be authentically digital, avoid mimicking physical motion. If you want to be fast and fluid, ensure your animations are independent and rendering at 60 frames per second.

Reference (HTML)

http://msdn.microsoft.com/en-us/library/windows/apps/hh465209

Reference (XAML)

http://msdn.microsoft.com/en-us/library/windows/apps/hh465209