C in CRUD for Silverlight
I don't think it's best-practice to put any logic that isn't strictly presentation-specific directly into a code-behind event handler like this, let alone that a UserControl knows anything about any DomainService1 object.

If you're shooting for best-practices, you need to look into the Model-View-ViewModel pattern; it's not the job of any UI component to perform any kind of business or data logic.