Using graphics for representing ideas is quite usefull and the "DnD idea" is really good. Dragging and dropping represents the idea of adding, moving or sending information from a source to a target. I've been playing with this idea this week and I'm happy with this preview. There are bugs, I found two, Cursor bug, doesn't change when starting dragging and drag-begin bug that doesn't call the IDraggable.DragBegin when should be.
I did an implementation based on a mix of Gtk#'s and System.Windows.Forms' DnD methods, comments are allowed and hearing/reading them would be very nice. The idea using two interfaces that represent the Draggable and the Droppable shapes, current implementation is
I did a sample screencast.