I just finished a trip from Atlanta to Moab, and then the Grand Canyon and the Arizona Strip via the mountains through Mesquite. Details at the following link.....
http://www.expeditionportal.com/forum/showthread.php?t=77551
The video link in the report above (climbing the mountain from Mesquite) was also shot on an iPad3, which has good camera and video capabilities.
We relied on the iPad, and yes I mean relied on it. There were times when we commented that we would have been hosed without it. For off-road and off-line navigation, it is important to have the iPad versions with cellular capability. The wifi only versions do not have capabilities beyond cell coverage, and I don't believe have true gps. The gps in the iPad3 (and iPad2) with cellular are very accurate, more than accurate enough for off road trails (screenshots attached).
I used GaiaGPS and GPSKit HD, and like them both. Both have different choices of maps, which I found useful.
I have attached two screenshots from the trip (GaiaGPS), to show the topomap. The second screenshot is a closeup of the two recorded tracks to show the accuracy (the green and blue recorded tracks (recorded separately) are virtually on top of each other, and both are directly on top of the road). At least two tracks were made that we're over 6 hours long. No breaks in the recorded tracks or issues were noted at any time during the recorded trips.
For street navigation you can download TomTom or similar. The large bright and high resolution screen of the iPad, choice of off-line mapping and tracking programs and maps, is the way to go in my opinion for vehicle navigation.
You can also use it as a gyro!
Caveat - navigation redundancy is advisable.