I have posted an MSI that will install XML files that will help you when programming Extensibility features. When installed, you will get more information in the tool tips when programming extensibility types. If you program against any of these Assemblies:

 EnvDTE.dll
 EnvDTE80.dll
 Extensibility.dll
 Microsoft.VisualStudio.TemplateWizardInterface.dll
 Microsoft.VisualStudio.VCCodeModel.dll
 Microsoft.VisualStudio.VCProject.dll
 Microsoft.VisualStudio.VCProjectEngine.dll
 Microsoft.VisualStudio.VSContentInstaller.dll
 Microsoft.VisualStudio.VSHelp.dll
 Microsoft.VisualStudio.VSHelp80.dll
 VSLangProj.dll
 VSLangProj2.dll
 VSLangProj80.dll

then you may wish to install these files. I created a new GDN workspace at http://workspaces.gotdotnet.com/VSExtTools where you can download this file.