Metro is the codename for the Open Packaging Conventions (a ZIP-based container convention for file format packaging) and the XML Paper Specification (a fixed format document specification based on XAML). Feng Yuan, one of the technical leads in the team has just started a blog and has been furiously blogging explanations and code samples. If you're an ISV building managed or unmanaged applications that need to print, save files or create a portable viewer, you should check out his blog.