Yes, I think that every city should have it. For some cities, e.g. New York, it would obviously be easier to pass. I think that if a cab picks me up on the street, the driver should know where I'm going, and the best way to get there - without typing it into the mobile phone, and constantly pressing the buttons while s/he's driving. Eventually it's going to be replaced with apps, but there are quite a few more pieces missing (e.g. real-time traffic information, frequent updates of road works, and (probably most important of all) perfect voice input/search/commands).