Tell-All Telephone [zeit.de] demonstrates how well one can be geo-located purely by mobile phone logs.
German politician Malte Spitz sued his mobile provider to receive his personal phone data of over 6 months, to prove how this information, combined with other publicly available facts, such as from Twitter feeds, blog entries and website stories, can reveal much more than one wishes for. German newspaper "Die Zeit" and computational journalism company OpenDataCity then rendered this data on an animated map with interactive timeline.
As a result, one can discover where Spitz was, when he worked or when he slept. All in all, it almost reveals an entire life.