How to Display an Assembly in the Add Reference Dialog Box

It is a common misconception, and one I also held, that components added to the GAC automatically appear in the .NET Add Reference Dialog. I guess this is a hangover from seeing registered COM components automatically appear in the add references dialog for all those years.
No, instead, you have to furtle around in the registry to make it happen, as "How to Display an Assembly in the Add Reference Dialog Box" describes. Very 1998.