This is a game changer. I'll put up with the washed out colors and poorly contrasted controls in VS2013 simply because of this tool. Useful for mind-mapping workflow scenarios and cross training other developers to pick up someone else's code.
Do not like the fact that when you move the elements of the diagram around the changes are lost.
Also, it it seems that if you save the diagram to the solution, that diagram is used again. You don't get a fresh start, you have to put up with the existing method calls, even though you do not want to see them..