The official support for PCLs from Xamarin is due in Alpha any day now - expect it before the end of June 2013.
Until then, you can see how to use PCLs by including the shim assemblies from MvvmCross - take a look at:
- the
PortableSupport
shims source - https://github.com/slodge/MvvmCross/tree/v3/PortableSupport - the Nuget 2.5
PortableSupport
package - https://www.nuget.org/packages/MvvmCross.PortableSupport/ - the 25 videos on http://mvvmcross.wordpress.com/ all of which use PCLs
- the accompanying source code for those videos - the .csproj files will show you how the shims are used - https://github.com/slodge/NPlus1DaysOfMvvmCross
- lots of other PCL based x-plat samples on https://github.com/slodge/MvvmCross-Tutorials/
For additional shims, watch questions like TPL on PCL for MvvmCross for PCL Profile 78 (I know people have got this working - just waiting for them to answer the question...)
When Xamarin official PCL support ships then I anticipate that they will ship official shims and we can retire the MvvmCross ones. However, no-one at Xamarin has given me any answer about this - for latest on this, maybe see status of https://bugzilla.xamarin.com/show_bug.cgi?id=8035