Starting from his Windows Phone 7 application, Visual Studio Achievements, developer Dan Delimarksy has written up his experiences of porting the code to a metro-based Windows 8 application.

One of the great features that is currently highlighted for Windows 8 and specifically WinRT is the low barrier of entry for existing Windows Phone and Silverlight developers in general. There was already a case of an existing Windows Phone application being ported to the new OS, but I decided to actually document the entire porting process in its core.

The first part is here, and the the full list of articles is on Delimarksy's website.