  We analyze the luminosity function of the globular clusters (GCs) belonging
to the early-type galaxies observed in the ACS Virgo Cluster Survey. We have
obtained estimates for a Gaussian representation of the GC luminosity function
(GCLF) for 89 galaxies. We have also fit the GCLFs with an "evolved Schechter
function", which is meant to reflect the preferential depletion of low-mass
GCs, primarily by evaporation due to two-body relaxation, from an initial
Schechter mass function similar to that of young massive clusters. We find a
significant trend of the GCLF dispersion with galaxy luminosity, in the sense
that smaller galaxies have narrower GCLFs. We show that this narrowing of the
GCLF in a Gaussian description is driven by a steepening of the GC mass
function above the turnover mass, as one moves to smaller host galaxies. We
argue that this behavior at the high-mass end of the GC mass function is most
likely a consequence of systematic variations of the initial cluster mass
function. The GCLF turnover mass M_TO is roughly constant, at ~ 2.2 x 10^5
M_sun in bright galaxies, but it decreases slightly in dwarfs with M_B >~ -18.
We show that part of the variation could arise from the shorter dynamical
friction timescales in smaller galaxies. We probe the variation of the GCLF to
projected galactocentric radii of 20-35 kpc in the Virgo giants M49 and M87,
finding that M_TO is essentially constant over these spatial scales. Our fits
of evolved Schechter functions imply average dynamical mass losses (Delta) over
a Hubble time that fall in the range 2 x 10^5 <~ (Delta/M_sun) < 10^6 per GC.
We agree with previous suggestions that if the full GCLF is to be understood in
more detail GCLF models will have to include self-consistent treatments of
dynamical evolution inside time-dependent galaxy potentials. (Abridged)
