The Forms.Init method has a parameter which can be used to specify assemblies containing renderers. This parameter is very important when using 3rd party views/renderers or a complex project structure where some renderers are in different assemblies.
public static void Init(IActivatedEventArgs launchActivatedEventArgs, IEnumerable<Assembly> rendererAssemblies = null);
However currently this parameter does not work for services, so the [Dependency(Serviceclass)] attribute can only be used in the main assembly. I think this is a severe problem for PCL projects where you might want to use MVVM like platform independent services without needing to use another dependency injection service.