High temperature superconductors (HTS) are an ideal class of
materials with which to study electronic correlations because the correlations can be tuned
from weak to strong via chemical doping. One of the most important questions in
HTS is how the superconducting state differs from that of conventional BCS
superconductors as a result of strong correlations. In this talk, I will
discuss the influence of disordered (glassy) magnetic moments on the
electronic spectrum in the superconducting state, with particular emphasis
on recent superfluid density measurements.