The blogosphere seems to be ablaze with news that iPhones keep track of all the locations you visit and store this information in an unencrypted file on your desktop when you sync with iTunes. A small application can be downloaded here that will plot that data against a map of the world.
Here’s a screenshot I just took, zoomed in to Italy, which shows all my recent travels. The implications on privacy issues are interesting, but do not expect too much. It looks like localization via GSM triangulation (the GPS coordinates are apparently not saved) is not very precise, as the map below includes a number of locations where I have never been, and does not include a number I have definitely been to.