Got an iphone?
Running iOS4 ?
If you answered yes to both of the above questions, then I think that it's only right that you are aware of the following.
Ever since you upgraded to iOS4, your iphone has been storing detailed information of your whereabouts, (latitude and longitude along with timestamps) and saving this to a little hidden file called "consolidated.db".
The good news, if you can call it that, is that the data does not seem to leave your phone.
Apple is still yet to comment on this issue, however it appears that it has been implemented internationally.