It's toggleable. The default right now is opt-out. But I think it can be made opt-in for logged in users and opt-out for anons (to make them remember and notice

It's toggleable. The default right now is opt-out. But I think it can be made opt-in for logged in users and opt-out for anons (to make them remember and notice where they came, most don't even notice the url when searching the internet).