When Google (GOOG) released Google Maps Navigation for Android it knocked 20% off the value of big turn-by-turn navigation players TomTom (TMOAF) and Garmin (GRMN) in a single day. Since then, Google Maps has spread to other mobile platforms like iOS, and its accuracy and usability has improved.
So we ask, why would someone pay hundreds of dollars for something we all can get for free? Sure, there are weaknesses with Google Maps, such as the need for cellular service, but it is now possible to load up a map and directions before a journey. Standalone GPS devices simply don't offer enough extras to make them a worthwhile buy anymore.