As a developer I'd like to make a few little utilities for myself that use private methods, etc. as I have no intent to submit them to the app store. For instance, at the moment I want to work on an inter-device communication tool (including an iPhone MiFi type implementation).
So the question is, does access to that particular functionality require a jailbroken device? Or are things like that just a matter of using unpublished APIs and such?
Well, based on some class-dump snooping it looks like the Wi-Fi and tethering methods are called on Springboard.app (except for the socks proxy method mentioned by Kristopher Johnson) which requires using the Mobile Substrate libraries and therefore requires Jailbreaking. Boo.