I remember what the Notification method was for now. It was for linked components, say you have component A which has a property of component B (think DataSet and Connection) if you remove the B component from the Form the Notificaiton gets fired to inform other components of the change. I most cases this involved setting a property to nil (which the object inspector would detect).

There is a great book "The Hidden Paths of Delphi 3" by Ray Lishner which goes into programming components and pl;ugins for the Delphi IDE. Although it is way out of date, much of what it goes into is still viable for delhpi 2005/2006 and it a gold mine a information.