  Studies of nearby elliptical and S0 galaxies reveal that roughly half of the
low mass X-ray binaries (LMXBs), which are luminous tracers of accreting
neutron star or black hole systems, are in clusters. There is a surprising
tendency of LMXBs to be preferentially associated with metal-rich globular
clusters (GCs), with metal-rich GCs hosting three times as many LMXBs as
metal-poor ones. There is no convincing evidence of a correlation with GC age
so far. In some galaxies the LMXB formation rate varies with GC color even
within the metal-rich peak of the typical bimodal cluster metallicity
distribution. This provides some of the strongest evidence to date that there
are metallicity variations within the metal-rich GC peak, as is expected in
hierarchical galaxy formation scenarios. We also note that apparent
correlations between the interaction rates in GCs and LMXB frequency may not be
reliable because of the uncertainties in some GC parameters. We argue in fact
that there are considerable uncertainties in the integrated properties of even
the Milky Way clusters that are often overlooked.
