iOS4 devices track and store their location
According to a presentation by two UK researchers at Where 2.0 conference, iOS4 devices constantly track and timestamp their location and dump that data into a file, which is shared with your desktop computer if you choose to backup your iPhone’s content. This presents a major potential for privacy breach.
For some phones, there could be almost a year’s worth of data stored, as the recording of data seems to have started with Apple’s iOS 4 update to the phone’s operating system, released in June 2010.
More information at O’Reilly.