Yeah, there is no way Google will magically start charging for services that have been free for years. The Nav is simply googlemaps.com with turn by turn directions added in.. granted, that's a big add in, but to start charging now or later, especially after sucking customers in with all free google products would be the worst business model ever.
I worried the same thing about Google Voice though.. Now that I'm suing nothing but it, I still have a nagging fear that years down the road it will become so full featured that I'll have to pay one bill to verizon and one to Google each month to keep my number!
But no, I don't see that happening either, as it's been said.. Google makes money from ads, and makes BILLIONS