Multisite phosphorylation is a common form of post-translational protein regulation which has been used to increase the switch-like behavior of the protein response to increasing kinase concentrations. In this talk we show that the switch-like response of multisite phosphoproteins is strongly enhanced by non-essential phosphorylation sites, a mechanism that is robust to parameter changes and easily implemented in nature. We describe analytic estimates for the Hill exponent of the switch-like response and suggest a possible evolutionary mechanism for the relatively large numbers of phosphorylation sites found in various proteins.