I'm not sure when this option became available but for future reference, Kent, you don't need to duplicate faces from one side and then scale x -1. You can just select that box ctrl+l and then use symmetrize under the mesh menu. Just saves a little bit of time :)
Oooo thanks for the tip! Ah must have been me, but selecting the face, duplicating and doing scale x -1 didn't work for me so I did Caleb's way. Hmm, seems like I have to do it for all of the faces though if I want the symmetry everywhere. (Luckily, we only have to do the places where the cameras sees teehee)