I don't know if I have, to be honest. I've seen some very short clips of people supposedly mapping certain exaggerated facial movements to cartoon avatars that look nothing like them. I guess I don't think that Facebook's solution will be a replacement for the real thing. I think we may get there once we have 3d cameras that can saturate a room, and glasses/contact lens/retinal displays.
I think it'd be extremely interesting to see how it compares to real life, vid calls and other alternatives.