Hey all,
I just released an addin to Xamarin Studio called "Project Linker". This addin was developed in order to automatically create and maintain links from a source project to a set of target projects, in order to make code sharing between different plataforms a more friendly task. It is based on the Visual Studio Project Linker extension.
It is available on the official addins repository, at http://addins.monodevelop.com/Project/Index/89, and the project page is http://rafaelsteil.github.io/monodevelop-project-linker/
I think it can be really useful to those not using PCL. The project is open source.