I completely agree with the above statement. Having all keyboard shortcuts toggle between the previously use tool and that shortcuts tool doesn't make workflow any easier. At least for me. Perhaps the option to turn that function on an off would be useful to people.
Additionally, having to press ⌘ D twice in order to deselect something is a bit of a pain. It slows down workflow. Although I can see how in some cases having a two step deselect can be useful. Perhaps alternatively you could press ⌘ D for a two step deselect and SHIFT ⌘ D to deselect everything.
Idealistically giving the user the ability to define their own keyboard shortcuts would be extremely helpful.