I did not get the NAV and honestly do not miss it! I have a TomTom but have not used that much.
I do use allot of the Turn-By-Turn directions via Sync. Works great! I have the Sync Destinations app on iPhone with all my saved points. If I need to use them or something new, I shoot it over to Sync from the phone. Than once in the car I go to Sync services and it downloads the directions to the car.
The only down side is if you go off the down loaded route. It will than ask you if you want to update the route and then go through the down load process again. Obviously not as fast as my TomTom if I change my route.