This sort of setup can also be used to monitor aircraft squelches. I got a few Raspberry Pis during a B1G1 sale, so I have one of these setups at work and at home. I like watching the planes as they take off from the local airport and queue up for arrival, and also seeing the nightly freight flights.

More info here: http://flightaware.com/adsb/piaware/

You can feed into sites like Flightaware and FlightRadar24 and get accounts with them that normally cost a lot for free.