I am doing some research on porting an old WPF app in a way that we could have a common layer for the Model and ViewModel so we can have an Android app using Xamarin Forms (maybe later iOS) and a WPF app for Windows 7 users.  The DataForm would be perfect.  Is it possible to have data annotations that would work for both or do you have to duplicate effort here.

Hello Jon,

Thank you for contacting us! Yes, you can share the viewmodel between WPF and Xamarin Forms apps.
Our Xamarin Forms components share their code through portable libraries including the attributes used by DataForm. 

In order to us the attributes you would need to add reference the the following assemblies and its xamarin dependencies if needed:
 - Telerik.XamarinForms.Common.dll
 - Telerik.XamarinForms.DataControls.dll

Please, find the iamgeof the portable profile that these assemblies support -http://screencast.com/t/JhJZlQOWLj

Regards,
Tsvyatko
Telerik