I still think it would be amazingly useful to be able to store and cache an area on google earth on your phone for offline use (say 10 mi x 10 mi max zoom and another few miles moderate zoom) that would work with GPS (either manual entry or through phone gps) to find your location on the map. Then you can literally have a birds eye view of the area you're in. If weather is bad, what's down that trail to the left? The right? Oh an abandoned cabin! lol
Although I don't have an iPhone, I do have an Android based phone which allows Google Maps to be auto cached offline. This is a handy feature as the cached area can be be significant in size and it also captures satellite view data.
With Google maps version 5.7 or higher, there is also the built-in functionality to cache user specific map sections for offline use. In summary, you long press on a spot of the map you want to cache then select an option that will then cache a 10 square mile offline map to your phone. I have not played around with this feature as much and appears it only caches street map data and not terrain or satellite view data.
And while these are both nice features to have, I would not bet my life on either as like anything electronic, the phone/batteries could fail at the worst possible time and right when you may need it the most.