Invisible computer graphics

When we think about digital effects in movies and TV shows, we usually think of scenes that are obviously impossible. For example, we remember watching aliens blow up the White House, or Neo dodging bullets.

However, modern computer graphics are so easy and inexpensive that they can replace entire outdoor sets even with a low-end TV budget. Why bother worrying about weather conditions and time of day when you can just film the whole scene in a sound stage and add the background later?

Here's a demo reel from a company that specializes in this technology:

The most striking example of this recently was the film Benjamin Button -- I remember walking out of it and telling my friends that it had the best special effects I had ever seen. Most of them replied, "Special effects? What special effects?" Not only were many of the environments digitally created, but so was the main character! Even for a graphics programmer, it was almost impossible to tell what was real. Click here for a video about how that was done.

It's useful for game developers to learn about film special effects because many of the same technologies can be used for pre-processing steps in video games, such as global illumination, fire and water effects, and performance capture. Can you think of any other examples of invisible computer graphics in movies?