The successes of ideal hydrodynamics in describing Relativistic Heavy Ion Collisions (RHIC) data at lower $p_T$ region led to the well known announcement that "RHIC Scientists Serve Up Perfect Liquid" (the Quark Gluon Plasma, QGP). In order to answer "How perfect is the QGP fluid?", one needs to extract the QGP viscosity from experimental data. In this talk, I will report recent progresses on viscous hydrodynamics + hadron cascade hybrid approach and show the new extracted QGP viscosity from RHIC data with a reliable uncertainty estimation. Then I will discuss the QGP viscosity at LHC energies.