Interesting website...

http://live.airportnetwork.com/sfo/

This feature allows you to watch the movement of flights and air traffic patterns currently in use within the Bay Area. This map will show flight tracks of aircraft arriving and departing from SFO, Oakland, and San Jose Airport and other nearby general aviation airports. Red plane icons are arrivals, green are departures, black are General Aviation or small propeller aircraft and helicopters. The white icons are aircraft transiting the area and bypassing local airports. The icon sizes are uniform regardless of the actual size of the aircraft.

These flight tracks, although taken from actual radar data, are not in real time. There is a delay of ten minutes, as indicated in the lower left corner of the map window. This can be helpful if you notice an unusual overflight in your neighborhood and you need time to bring up this website to study its altitude and flight path. It is not uncommon to see tracks occasionally disappear as the information is updated.