This talk is a survey of recent advances in the Pugh-Shub stable ergodicity theory for partially hyperbolic diffeomorphisms. I describe two "competing" methods to show that a given partially hyperbolic diffeomorphism is stably ergodic (i.e., it is ergodic along with any of its sufficiently small perturbations). One of them relates the problem to the global estimates of the action of the system along its central direction while another one deals with a more delicate estimate using Lyapunov exponents in the central direction.