Recently I was looking for a way to create an Adding that will add a Context Menu only when I Right Click on .xaml files.
I know there a many ways now, but I still love using VS studio addins for some simple tasks.
In case you are wondering how to do that
I found this great article: http://davedewinter.com/2008/03/22/dynamic-menu-commands-in-visual-studio-packages-part-2/