Google Maps Navigation is one of the stand-out features of the Motorola DROID, and thanks to Google's recent efforts those of you with Android 1.6 devices can run it too. The proviso is always that you must be in the US to take advantage of the beta; that hasn't stopped Electricpig from throwing together a hacked version that will work on non-US Android handsets.
One of their readers has worked out how to install an almost fully functional version of Google Maps Navigation, lacking only voice command. Try to run that - the system accepts voice guidance prompts to set destinations - and the app crashes. It's probably because they're attempting to run the Android 2.0 version of the software on an Android 1.6 device; the 1.6 version of Google Maps Navigation lacks voice guidance.
They're promising a tutorial showing how to install it yourself, and we're now left wondering whether Google will take any action to curtail these unofficial installs. Android as a whole may be open-source and Google make plenty of positive noises about the developer community tweaking the OS; however, the search giant has also shown itself to be pretty protective of its proprietary software that runs on Android - such as the Gmail app - and as such Google Maps Navigation tweaking might fall outside of what it considers appropriate modification.
Update: Tutorial is here.