…comes courtesy of the 7th Circuit U.S. Court of Appeals, which has ruled that the government's surreptitious placement of a GPS device on a suspect's car and subsequent tracking of his movement is not a search for Fourth Amendment purposes, and doesn't require a warrant. The court did make some noise about the suspects being shady characters, but refused to require police to show "probable cause," due to the way the government framed its argument.
Other federal circuits have issued different rulings on the use of GPS devices, so it seems like an issue the U.S. Supreme Court might visit. Needless to say, a confirmation of the 7th Circuit ruling would be troubling, particularly given that we're headed for the day when all cars sold in the U.S. will eventually be equipped with GPS.
Wired News adds the punchline:
Bonus terror: wording in the ruling clearly indicates that the judges think that you can track GPS devices using Google Earth.