GPS: Not a City Kitty
Specifically, GPS doesn't work that well indoors or in built-up areas. If the three satellites needed to triangulate GPS positions cannot "see" the receiver, then errors are likely -- even when the receiver is aided by additional data from the cellular network.
This might not matter so much when you are using GPS to trace a truckload of indigestion tablets through the ring roads of Boston, but it's worth keeping in mind when location-capable handsets are being sold to anxious parents as potential child-tracking devices.
— Dan Jones, Site Editor, Unstrung