I use navigon on iPhone to replace my company owned Navigon 2100 when I left their employment and the iPhone actually has a larger screen then the dedicated PND it is replacing. The 1 week of overlap where I had both units showed them to be both about the same accuracy when placed in the same location attached to a mount on my windshield and the iPhone has the ability to announce turns through my car stereo to boot.

Smartphone Wins!!! *crowd goes wild*