I use my dongle for a "virtual radar" system:
ADS-B (Automatic dependent surveillance – broadcast) will eventually replaced ground-based radar for tracking aircraft. With the dongle and FREE software, you can track aircraft in your area. In my case, I can track aircraft about 200 miles away. Kewl!
Details here: http://forums.radioreference.com/air...ual-radar.html. A lot has changed in the software since I made that post, but the concept is basically the same.