Anyone's who's bought a car with a built-in nav system knows the pain of seeing their expensive accessory totally eclipsed by even the cheapest external GPS units just a year or two later -- everything from UI to multimedia integration progresses so fast it's almost not worth it. That might change soon, though -- Harman and Mercedes are working on a "hybrid" nav system that combines the easy replaceability of an external PND with the integration and sleek looks of a built-in system. The goal is to build a standard design that can upgraded quickly -- right now OEM systems have to be designed almost three years in advance -- so the screen and controls will be mounted on the dash in a cradle, while a second hidden "processing box" will handle the actual GPS system, music storage and
