There are SO many possibilities for this technique.
You can view my students' video all strung together in iMovie at the link above as well.
These tutorials show how to create our award winning Fugleflick, Careers in Art. This video was selected as the best student video of 2011 in the NextVista.org student contests.
This is the technique that helped us put STEAM in the McGraw-Hill Stemie Awards and $5000 in our school's bank account!
UPDATE: Carol shared her green screen + Doink animation with me below: