Read original post at Kraig Brockschmidt's Blog
We purposely included many talks at //build 2013 about performance because it's one area that's very important for all the apps you're creating as well as for consumers' overall experience of the system. Windows 8.1 Preview has better performance across the board, so in many ways apps just benefit without doing anything special. Then we're introducing more tooling around performance, and have more experience now at best practices for apps.