From the UK’s online Guardian publication:

    Security researchers have discovered that Apple’s iPhone keeps track of where you go – and saves every detail of it to a secret file on the device which is then copied to the owner’s computer when the two are synchronised.
    The file contains the latitude and longitude of the phone’s recorded coordinates along with a timestamp, meaning that anyone who stole the phone or the computer could discover details about the owner’s movements using a simple program.
    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.

There’s a photo on the linked site that shows an example of the GPS output of the secret file.

If you’re not doing anything wrong, you don’t have anything to hide, right?

Decide for yourselves if you want to put up with this.

Full disclosure: I am neither long nor short Apple.