This is admittedly disturbing news. Apparently, the iOS4 operating system periodically records your location information. It gets transferred to your computer when you sync, and it can be hacked by anyone who has access to your phone or computer.
Go ahead, try it. My computer generated the map below in about 20 seconds. The big blob on the center-right is Denver, but you can also see my travels to Boulder and some ski trips to Winter Park and Copper. Obviously, I don't mind if other people know about this information, but it's rather jarring to learn that this has been recorded without my knowledge by a company from whom I bought a phone.