The star formation activity of the host galaxies of active galactic nuclei provides valuable insights into the complex interconnections between black hole growth and galaxy evolution. A major obstacle arises from the difficulty of estimating accurate star formation rates (SFRs) in the presence of a strong active galactic nucleus. Analyzing the 1-500{mu}m spectral energy distributions and high-resolution mid-infrared spectra of low-redshift (z<0.5) Palomar-Green quasars with bolometric luminosity of ~10^44.5^-10^47.5^erg/s, we find, from comparison with an independent SFR indicator based on [NeII]12.81{mu}m and [NeIII]15.56{mu}m, that the torus-subtracted, total infrared (8-1000{mu}m) emission yields robust SFRs in the range of ~1-250M_{sun}_/yr. Combined with available stellar mass estimates, the vast majority (~75%-90%) of the quasars lie on or above the main sequence of local star-forming galaxies, including a significant fraction (~50%-70%) that would qualify as starburst systems. This is further supported by the high star formation efficiencies derived from the gas content inferred from the dust masses. Inspection of high-resolution Hubble Space Telescope images reveals a wide diversity of morphological types, including a number of starbursting hosts that have not experienced significant recent dynamical perturbations. The origin of the high star formation efficiency is unknown.