Senseable City Lab from the MIT brought up several projects that explore the real time traffic data from wireless communications to map "chat" activity in a city. Check iSpots, Graz and Real Time Roma as examples.
Now as part of the same Lab the MIT is making the source code of its iFind project available through GPL.
With iFind "you and your buddies can instantaneously exchange your locations on campus, talk to users nearby, and microcoordinate more effectively."
First on CNet. Covered also at WirelessIQ,
And here is the reason why your GPS got a bit lost last week, according to this article from ABC:
The major activity happened around Dec 6th according to this article.
"[...] communication with GPS navigation satellites in the lower ionosphere was blacked out for up to two hours."