The Portable Class Library (PCL)
The portable Class library (PCL) will allow us to share a large part of the code across projects.
It is possible for a few years to share the PCL code between projects (Sliverlight and WPF, Windows Phone, Windows 8,…).
More projects are different, the more shared classes decreases.
It is important to see that this Library can be used for projects compatible with the selected options.
Note also the visual studio Express editions do not create a PCL, but instead accepts their use in a project.
This Library may use a library which would not have at least the same options selected.