  We have obtained high signal-to-noise spectra along the major axes of 28 S0
galaxies in order to search for the presence of disk stars on retrograde
orbits. Full line-of-sight velocity distributions were extracted from the data,
and the velocity distributions were modelled as arising from the superposition
of populations of stars on prograde and retrograde orbits. We find no new cases
in which a significant fraction of disk stars lie on retrograde orbits; an
identical analysis of NGC~4550 does reveal the previously-known
counter-rotating stellar disk in this system. Upper limits determined for each
object indicate that no more than about 5% of the observed disk star light
could arise from counter-rotating stellar components. These results suggest
that previously-discovered disk galaxies with counter-rotating stars are
exceptional and that (at 95% confidence) at most 10% of S0 galaxies contain
significant counter-rotating populations. The most likely value for the
fraction of such S0 galaxies lies closer to 1%. This result contrasts with the
prevalence of counter-rotating gas in these systems; combining our new
observations with existing data, we find that 24+/-8% (1-sigma error) of the
gas disks in S0 galaxies counter-rotate relative to their stellar components.
