  The value of the dynamic critical exponent $z$ is studied for two-dimensional
superconducting, superfluid, and Josephson Junction array systems in zero
magnetic field via the Fisher-Fisher-Huse dynamic scaling. We find
$z\simeq5.6\pm0.3$, a relatively large value indicative of non-diffusive
dynamics. Universality of the scaling function is tested and confirmed for the
thinnest samples. We discuss the validity of the dynamic scaling analysis as
well as the previous studies of the Kosterlitz-Thouless-Berezinskii transition
in these systems, the results of which seem to be consistent with simple
diffusion ($z=2$). Further studies are discussed and encouraged.
