It seems that the next frontier of popular data visualization might focus on the usage tracking data that is generated by default by the powerful sensing device in your pocket: the smart phone. Several iPhone/Android projects visualizing usage data are currently in some hidden alpha phase, though a few early experiments have recently seen the light in some way or form. I guess you will either love this new development, or will start hiding your backup files for any person with access to your computer.
iPhone Tracker [petewarden.github.com] reveals all the information that the iPhone is continuously storing about its geographic movements, (seemingly) regardless of the apps running. So, no separate app need to be installed or run on the phone, as it simply visualizes the geo-location usage data that is already captured and stored in the backup files. Videos of the resulting maps can be watched below, while the application and its source code is free and available for download.
Similarly, Mobile Report [datalysed.com] has cracked yet another iPhone backup file, this time to show a timeline with the patterns and statistics about your historical telephone calls. It can be used by submitting your own file via a web form.
Also via Wired and Engadget and The Guardian. See also What a Provider's Mobile Phone Logs Reveal about You.