A substitute for GPS
From Techcrunch: Google Mobile Maps PinPoints Your Location Without GPS
This technology uses cell phone towers (and triangulation) to locate you. While not as perfect as GPS, it should be useful for general navigation, especially with added algorithms to smooth out the jumpyness. It is an idea long speculated on (in the transportation community see: this article by my late colleague YB Yim for a review and this for one of the earliest papers on the idea. ) that is finally seeing commercialization.