  We use Quantum Monte Carlo to evaluate the conductivity $\sigma$ of the
2--dimensional disordered boson Hubbard model at the superfluid-bose glass
phase boundary. At the critical point for particle density $\rho=0.5$, we find
$\sigma_{c}=(0.45 \pm 0.07) \sigma_{Q}$, where $\sigma_{Q}= e_{*}^{2} / h$ from
a finite size scaling analysis of the superfluid density. We obtain
$\sigma_{c}=(0.47 \pm 0.08) \sigma_{Q}$ from a direct calculation of the
current--current correlation function. Simulations at the critical points for
other particle densities, $\rho=0.75$ and $1.0$, give similar values for
$\sigma$. We discuss possible origins of the difference in this value from that
recently obtained by other numerical approaches.
