"Proporta do seem to snap up some of the best accessory ideas. They've just launched a 'Keychain GPS', weighing only 30g, with SiRF III chipset and USB (and 12V) charging. They claim it'll work from within a pocket, briefcase or handbag, meaning that provided you remember to keep it charged, you can pretend your Bluetooth-equipped smartphone has its own, private, invisible GPS."
This looks pretty slick. After trying using GPS with my Smartphones though I have become pretty convinced it is not very practical. The small screen makes watching a map pretty difficult. If you are trying to watch that little screen while driving it can be rather distracting.