We may have seen some of these before:
Aspiring scientists from the Zurich School of Applied Sciences have built a video simulation that displays the flight path of every commercial flight in the world over a 24-hour period. There isn't much of an application for it, but it sure is cool to look at.
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Below: This one shows traffic into and out of Atlanta. Keep in mind that Delta operates the world's largest hub here.
Below: Flight activity for all U.S. FedEx flights
Below: Flight activity over Europe. This one takes a minute or two to load, but it's worth the wait.
http://blog.wired.com/cars/2008/12/earlier-this-ye.html