Ever wanted to know from an add-in whether a context Guid of the EnvDTE80.ContextGuids class, for example vsContextGuidDebugging, vsContextGuidDesignMode, vsContextGuidSolutionExists, vsContextGuidSolutionHasMultipleProjects, vsContextGuidSolutionHasSingleProject, vsContextGuidNoSolution, etc. is active? This new article of mine shows how:

HOWTO: Use the IVsMonitorSelection interface from a Visual Studio add-in
http://www.mztools.com/articles/2007/MZ024.htm