  We report recent progress on causal viscous hydrodynamics for relativistic
heavy ion collisions. For fixed specific shear viscosity eta/s, uncertainties
in the elliptic flow arising from initial conditions, equation of state, bulk
viscosity and numerical viscosity, and the treatment of the highly viscous
hadronic stage and freeze-out procedure are analysed. A comparison of current
viscous hydrodynamic results with experimental data yields a robust upper limit
eta/s < 5/(4pi).
