Well, not really. mmalc's GraphicsBindings has a JoystickView which
seems to maintain KVO by using a setValue:forKeyPath: as the last
step in processing a mouse click. But it's trivial because the
value being observed is only a single value, not an array, and not
generated on the fly.
For anyone looking further into this sort of app, there’s also
AXCanvas in /Developer/Examples/Accessibility. It’s a fairly good
showcase for what you can do with KVO, especially in the undo
management department.
