Microsoft has published a series of WhitePapers for Windows 8 Developer Preview on the new Windows Dev Center.
There are three examples of documentation available on the page:
This paper provides a set of network considerations that every connected Metro style app should know about.
This paper provides information about the invocation and dismissal behaviors of the Touch Keyboard (TKB) for Windows operating systems. It provides guidelines for developers to understand how the TKB shows and hides itself.
Downloadable white papers
The Windows Developer Preview introduces a number of new APIs to enable Play To and home media sharing experiences in Metro style apps. This white paper provides an overview of these new APIs along with some examples and guidance on how to enable Play To and media sharing in Metro style apps.
This white paper provides an overview of background tasks for Metro style apps.
This white paper provides an overview of handling sensor input for motion and device orientation.
This paper provides information about the Windows App Certification Kit (ACK) and its use in the various app certification programs for Windows. It provides guidelines for developers for usage of the kit and the associated certification processes.