I think that I have found one of the best articles on MVVM that I have ever read:

http://jmorrill.hjtcentral.com/Home/tabid/428/EntryId/432/MVVM-for-Tarded-Folks-Like-Me-or-MVVM-and-What-it-Means-to-Me.aspx

This article sums up what is in MVVM and what is outside of MVVM. Note, when I and most other people say MVVM, they really mean MVVM, Commanding, Dependency Injection + any other Patterns you need to create your application.

In WPF a lot of use is made of the Decorator and Behaviour pattern as well. The goal of all of this is to have pure separation of concerns. This is what every code behind file of every Control / Window / Page  should look like if you are engineering your WPF and Silverlight correctly:

C# – Ideal

  public partial class IdealView : UserControl
  {
      public IdealView()
      {
          InitializeComponent();
      }
  }

Figure: This is the ideal code behind for a Control / Window / Page when using MVVM.

C# – Compromise, but works

  public partial class IdealView : UserControl
  {
      public IdealView()
      {
          InitializeComponent();

          this.DataContext = new IdealViewModel();
      }
  }

Figure: This is a compromise, but the best you can do without Dependency Injection

VB.NET – Ideal

Partial Public Class ServerExplorerConnectView

End Class

Figure: This is the ideal code behind for a Control / Window / Page when using MVVM.

VB.NET – Compromise, but works

Partial Public Class ServerExplorerConnectView

    Private Sub ServerExplorerConnectView_Loaded(ByVal sender As Object, ByVal e As System.Windows.RoutedEventArgs) Handles Me.Loaded
        Me.DataContext = New ServerExplorerConnectViewModel
    End Sub

End Class

Figure: This is a compromise, but the best you can do without Dependency Injection