The simple answer is they can use this index to quickly find the user experience (UX) guidelines that can help you create a great Windows 8 style app.
This PDF file.
Windows 8 UI style apps are the focal point of the user experience on Windows 8, and great apps share an important set of traits that provide a consistent, elegant, and compelling user experience.
Use touch interactions that keep the user in control and confident, and leverage the screen or device edge so people can confidently find commands. See Touch interaction design.
These features help you create great experiences for every form factor and every viewing option your users have.
Contracts are the glue that binds Metro style apps together and to the system UI. Two apps that have implemented the same contract can work together to complete a broad or complex scenario. Some contracts are represented by charms. See a complete list of app contracts.
Capabilities identify the device features your app uses.
A tile is the front door into an app. Sitting on the Start screen, it is an extension of the app and can provide much more personal and engaging information than a traditional icon. Invest in designing a great tile to draw people into your app.
Provide fresh content through live tiles and notifications to let people feel connected to your app. Make sure you help your users connect with the people and devices that they care about.
Design your app's UI to showcase the content. Minimize distraction and help people get immersed in the content by leaving only the most relevant elements on screen. Following these guidelines will help you provide a consistent, elegant, and compelling user experience.
Text and input
Create a continuous experience across devices by roaming data and settings that lets people pick up a task right where they left off and that preserves the UX they care most about, regardless of the device they're using.
Every app should always have a solid foundation in order to reach as many people as possible.
Teaching Curricula see http://www.microsoft.com/faculty
Windows 8 resources for UK Developers see http://www.microsoft.com/uk/msdn/windows8
Windows 8 resources for Gaming Developer see http://www.ubelly.com/gaming
Holy smokes, this is a fantastic collection! I'll be linking to this via a blog post today at MicrosoftFanboys.com.