In 2005, Aaron Koblin took all of the air traffic over United States data, as seen by the FAA, and visualized it in a beautiful animation. Aaron's work was originally developed as a series of experiments for the "Celestial Mechanics" project (eye candy!) by Scott HEsels and Gabriel Dunne at UCLA.
The video clip above tracks all flights over the United States over a few days in March 2005, which brings this question to my mind: "where are all those people going?" Hit play or go to Link [YouTube] | Flight Patterns website