This is a great "behind the scenes" video by the production company Stargate Studios. It shows how popular television shows like 24, Ugly Betty, and Heroes use green screens in places where you would not think that special effects are involved.
My favorite scene starts about 30 seconds in. It's from Ugly Betty and she walks out of a building and smacks into a bus stop shelter. I figured they would at least built a real bus shelter for her to walk into and just insert a new background. But even the bus shelter is fake! In the green screen version she just walks into a small piece of plastic. Essentially everything is added "in post".
This insight into current TV production is a great complement to the Avatar behind the scenes video. Both illustrate different forms of virtual productions. In Avatar everything is virtual, the main characters and the whole environment. With TV shows we see they are mainly "faking" only the sets. For now.
The big question is, how many years until Avatar-style "performance capture" is used to generate an ordinary human character? Maybe it will first be done in a movie, but costs are always dropping so soon after they will start popping up on TV. This will be a big milestone: a virtual character on a mainstream TV show. Not a sci-fi show, but a drama or comedy, just another member of the cast.
For example we might see an older accomplished actor "driving" a younger version of themselves, or someone else entirely. A completely convincing virtual human performance is not that far away. And after the first one, many will follow. What will be the implications for actors? What about the the poor out-of-work plastic surgeons? It will be a strange and interesting future.