Disclaimer: I don't want you to "pwn" your iPhone. Pwnage is bad! It will void your warranty, Steve Jobs will loose weight because you do so and for every millionth iPhone pwned some wacko will torch the Apple facilities. So, just don't, okay?
Still, there might be reasons why a pwned iPhone might be interesting regarding GPS usage. First of all, there is an App that allows you to use Google Maps offline, but this might be interesting to those without an unlimited data plan only.
Then there is an App called "Insomnia". All it does is preventing the iPhone from going into suspend after the screen is switched off, thus allowing e.g. a tracking applikation like Path Tracker to track your journey after the iPhones screen was switched off. This might save some energy, but as the iPhone isn't able to suspend, it will still drown your battery.
Last but not least there is an application that is able to backup your program data, allowing to keep information stored after an update trough App Store. This isn't really a GPS related application, but still might be helpful.
Yeah, this is what you might get if you would pwn the iPhone. But, I'm sure you wouldn't. (At least, don't say I made you do so and especially don't blame me if something went wrong!)