  We argue based on theoretical considerations and analysis of experimental
data that quasiparticle excitations near the nodes determine the low
temperature properties in the superconducting state of cuprates. Quantum
effects of phase fluctuations are shown to be quantitatively important, but
thermal effects are small for $T \ll T_c$. An anisotropic superfluid Fermi
liquid phenomenology is presented for the effect of quasiparticle interactions
on the temperature and doping dependence of the low $T$ penetration depth.
