If you are interested in receiving ADS-B a/c plots and couldn't afford to buy a Kinetic SBS or AirNav Radarbox etc., there is away that you can join in this activity with a cheap RTL1090 dongle.
http://sonicgoose.com/using-a-rtlsdr-dongle-for-ads-b/
I have set up one of these RTL1090 dongles and while it isn't as sophisticated as the SBS-3, it will still give you an idea of what is flying in your location.
Cheers,
Noel