Professor Thibault have uploaded this video demonstrating turn by turn GPS navigation on Mango. While the UI is very attractive, the app has major (apparently intentional) flaws in functionality.
As we posted earlier, the voice directions are only delivered when the screen is tapped. Professor Thibault also notes the warning sound only sounds when one is at the turn itself, not providing any time to actually act and change direction. Lastly the text directions do not scroll automatically, making the app close to useless without constantly touching the screen.
As mentioned earlier, the issues may be due to Navteq’s license, but at this stage I do not really care who’s fault this is – Microsoft needs to fix it.