A new crop of web services in the U.K. allow you to locate and track people via their mobile phone. The phone companies themselves, and emergency call centers, and anybody else authorized, have long been able to do this in the U.S. and U.K. and elsewhere, but now it's going retail. There is also this service which at least alerts the trackee when his or her location is being queried. This partially addresses the attack of borrowing somebody's phone long enough to "give consent" and then tracking them with the service. Via Ian Grigg's Financial Cryptopgraphy.
Counter-intuitively, this development may enhance privacy, since the publicity that accompanies retail services will help prevent people from being in denial about the functions of their cell phone. Even if it doesn't enhance privacy in this manner, it may at least help take us from an Orwellian model of surveillance (the state behind a one-way mirror) to a Brinian model (peer to peer surveillance). OTOH, it may just fulfill the daydream of many a boss of being able to track employees 24x7.