  We compile black hole (BH) masses for $\sim 60,000$ quasars in the redshift
range $0.1 \lesssim z \lesssim 4.5$ included in the Fifth Data Release of the
Sloan Digital Sky Survey (SDSS), using virial BH mass estimators based on the
\hbeta, \MgII, and \CIV emission lines. We find that: (1) within our sample,
the widths of the three lines follow log-normal distributions, with means and
dispersions that do not depend strongly on luminosity or redshift;(2) the
\MgII- and \hbeta-estimated BH masses are consistent with one another; and (3)
the \CIV BH mass estimator may be more severely affected by a disk wind
component than the \MgII and \hbeta estimators, giving a positive bias in mass
correlated with the \CIV-\MgII blueshift. Most SDSS quasars have virial BH
masses in the range $10^8-10^9 M_\odot$. There is a clear upper mass limit of
$\sim 10^{10} M_\odot$ for active BHs at $z \gtrsim 2$, decreasing at lower
redshifts. Making the reasonable assumptions that the underlying BH mass
distribution decreases with mass and that the Eddington ratio distribution at
fixed BH mass has non-zero width, we show that the measured virial BH mass
distribution and Eddington ratio distribution are subject to Malmquist bias. A
radio quasar subsample (with $1.5\lesssim z\lesssim 2.3$) has mean virial BH
mass larger by $\sim 0.12$ dex than the whole sample. A broad absorption line
(BAL) quasar subsample (with $1.7\lesssim z\lesssim 2.2$) has identical virial
mass distribution as the nonBAL sample, with no mean offset. (Abridged)
