Installation process is pretty simple, you will need ClockworkMOD recovery on your Nexus S and rest is just some easy flashing. You can find the download links and full install instructions here (for I9020T) and here (for NS-4G).
PS: Only flash this if you really want Face Unlock, otherwise there is no other incentive for you.

One reply on “Nexus S gets AOSP based ROM with Face Unlock”
working fine … !!!