Insight into the nature of the pairing of charge carriers in high-Tc superconductors may be provided by a systematic investigation of the condensation energy. In this work we report on studies of the electronic kinetic energy across the complex phase diagram of these materials. The c-axis component of the electronic kinetic energy (determined from an analysis of the optical constants) is shown to be reduced below Tc, primarily in those compounds in which the superconducting transition at Tc is preceded by the formation of the partial gap in the density of states (pseudogap) at T*>Tc. An examination of the doping dependence of the infrared conductivity in conjunction with the results of photoemission spectroscopy suggests that the lowering of the kinetic energy is a property of the electronic states close to the intersection of the two-dimensional Fermi surface with the boundary of the Brillouin zone. We contrast the c-axis results with the energetics associated with the nodal quasiparticles probed through the in-plane conductivity.