Rephrasing the question to see if I get some views.
Following is how you would get the current solution directory from an add-in:
_applicationObject = (DTE2)application; // retrieved from OnConnection method
string solutionDir = System.IO.Path.GetDirectoryName(_applicationObject.Solution.FullName);
How would you do this via a VSPackage?
I'm migrating a visual studio add-in to a VSPackage as I'm intending to add some user controls that require a deeper integration with the IDE.
I found some good references on the relative merits of add-ins vs integration packages such as: http://nayyeri.net/visual-studio-addin-vs-integration-package-part-1
And some good tutorials on msdn on VSPackages such as: http://msdn.microsoft.com/en-us/library/cc138589.aspx
I haven't found a good reference yet (on msdn or otherwise) on how the higher level interfaces in add-ins (such as DTE) map to lower level interfaces in VSPackages.
Any good references out there to help with general mapping from add-in interfaces to VSPackage interfaces?