Just recently came across the fact that some methods are hidden from intellisense through the use of the [System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)] attribute. Two that are hidden are System.Windows.Threading.Dispatcher.CheckAccess() and System.Windows.Threading.Dispatcher.VerifyAccess().  These methods are handy when you have a multi-threaded WPF application and need to insure that you are on the UI thread before databinding or doing some other UI activity. A quick search using reflector didn't surface any other hidden WPF apis, although there are other hidden .NET apis.  Worth noting.