I was house hunting today around Melbourne and I was relying on my tablet (google maps) for navigation. I reckon it's probably the best mapping system there is (sat nav + 3g). Searching and navigation was a breeze. But.... it was such a cumbersome arrangement! I had to constantly charge it, fiddling it betwen the tablet and my radio (volume control), getting my partner to hold it and give me instructions (I obvbiously can't hold it or look at it while driving!). Once we park, we had to keep it inside the dash or bring it. Then get back in, set everything up for the next destination..
I got over it after the 3rd house inspection! I want full integration! It's just so much more convenient.
That said, google maps will always be a great back up, especially searching for specific stores/restaurants.
Note: I'm driving my corolla atm. I've got a jetta on order (missus got a polo on order).