I set up a static USB GPS receiver on an iBook running Linux. It recorded once a second for about 10 hours overnight. The graphs on the left are the frequency counts, the right are the measurements with time. The first row is latitude then longitude then altitude. Its obvious with the altitude one, but the others also have a range of about 100 meters and most measurements falling in a 10 meter area.
The last graph shows a plot of lat/long with time for the whole data sequence
Interesting that the noise in the lat/long is correlated but the altitude, apparently, is not.