title: Implementing INotifyPropertyChanged in a Model that is exposed in a collection
body: <p>I've got a Model class exposed in an ObservableCollection desgined with a DataTemplate where the Model's proeprty bindings are handled.</p>
  
  <p>When I implement the INotifyPropertyChanged interface in the Model class manually, the bound proeprty in the ObservableCollection doesn't change automtically, but only after re-rendering the collection.</p>
  
  <p>When I inherit from ViewModelBase (an MVVM Light toolkit class) and use the RasiePropertyChanged method, the bound property changes automatically without refreshing the entire collection.</p>
  
  <p>What does the ViewModelBase do except for implementing the INotifyPropertyChanged interface?  </p>