  We present an update of the MILC studies of the physics of light
pseudoscalars using improved staggered fermions. New runs at lighter quark
mass, as well as increased statistics for older sets, are enabling us to
improve the results for decay constants in full QCD. In addition, we have
analyzed quenched runs at two different lattice spacings. This makes possible a
test of the applicability of staggered chiral perturbation theory in a
different context.
