Frederico Regateiro wrote 2 nice articles on Visual Studio Visualizer.
The first part targeting ADO.Net objects is available from http://www.codeproject.com/Articles/578777/Visual-Studio-Visualizer-Part-1
The second part targeting Entity Framework objects is available from http://www.codeproject.com/Articles/584739/Visual-Studio-Visualizer-Part-2-Entity-Framework