Ok, here it goes...
I absolutely love my iPhone (it is in almost every way better than my old android) but as mentioned, the navigation is not even close.
I have tried Waze, Motionxgps and map quest and honestly hate all of these apps. Motionx has the best UI, but I believe that all 3 of these apps get directions from the same place and use the same service. Here's what I mean, I find that each of these apps extremely slow to reroute (I will will literally be driving 30seconds before the gps re-rerouts me. The gps does not seem accurate at all in any of these apps and often keeps me on my continued path even though I have diverged from it. Just overall terrible. And the UI on all 3 absolutely sucks
The maps app on the iPhone which uses Google maps is actually extremely accurate. It tracks my motion incredibly smooth and instantly updates where I am. This leads me to believe that the GPS hardware is just fine in the iPhone. Of course the maps app does not do turn by turn so I find it pretty much useless - but it is really good if I am say walking around NYC.
Naviagation is the one thing I miss about android and despite what people say, I believe it is a very important aspect of a smartphone. I hope apple updates with something soon - or if anyone has any other gps recommendations let know - but again (the 3 I have tried have terrible UI, give bad directions, take forever to reroute and are not smooth at all in updating my location status)