When you hit the ‘Geolocate Target' button, Creepy goes off and uses the services' APIs to download every photo or tweet they've ever published, analysing each for that critical piece of information: the user's location at the time. […]
When the software finishes its run, it presents you with a map visualising every location that it found - and that's when the hairs on the back of your neck go up. While the location of an individual tweet might not reveal much, visualising a user's history on a map reveals clusters around their home, their workplace, and the areas they hang out.
Call me crazy, but on my iPhone I always have Location Services set to "off."