I am going now to post some articles about common questions that appear in the MSDN VSX forum about the nodes of the Solution Explorer / Server Explorer and that I have noticed that I hadn’t addressed in my articles. The first one is about getting the selected node(s) in the Solution Explorer:

HOWTO: Get the selected nodes in the Solution Explorer from a Visual Studio add-in
http://www.mztools.com/articles/2013/MZ2013019.aspx