Living in the shadow of superintelligence

Although it regularly discusses the possibility of superintelligences with the power to transform the universe in the service of some value system—whether that value system is paperclip maximization or some elusive extrapolation of human values—it seems that Less Wrong has never systematically discussed the possibility that we are already within the domain of some superintelligence, and what that would imply. So how about it? What are the possibilities, what are the probabilities, and how should they affect our choices?