I ssh into my devices often, eg. to get pictures out, or to scp episodes into my vlc folder - since my goodplayer can't play mkv.
I am also pinging ocassionaly other servers and have to do it from another device than my iPad if it is not jailbreaked.
Imho, you all seem to be to accustomed to appliances - I favor open devices without those hastles. And being unable to inspect a good before purchasing it, if it is something lasting like software sucks.
Surely an Android device would have been a better choice? Jailbreaking is a kludge, it doesn't make the iPhone less encumbered from the average user's perspective.
(While a couple specific devices are open, most Android devices are closed; it does a disservice to connect the notion of "Android" with "open". Your point stands, however, with that detail fixed, although the process for setting up Debian or Ubuntu Core in a cheroot to get a nice ssh server with a decent shell and a package manager is a lot more complex than Telesphoreo on an iPhone.)
That done with, from the "average user's perspective", jailbreaking an iPhone 4 gets you more freedoms from less invested time and with less required knowledge than even a a "truly open" Nexus device: the tools are more centralized and easier to find how-tos that expect nothing more than "I sort of know enough to use YouTube", they are less technical to operate (and often even quite graphical; sometimes even having been embedded in web pages for a "slide to jailbreak‘ experience: I don't think I've ever seen a hack quite as smooth as comex's JailbreakMe 3.0), and due to Substrate it is infinitely easier to intstall the one or two custom changes you want rather than thinking about choosing and installing a custom version of the entire OS or having to screw around with risky patch files or incredibly complex baksmali instructions.
Like others have replied already to: look around on the system, to transfer media (mp3, documents, etc.).
I also used it to develop and learn the Objective-C on iOS. I didn't have a Mac at the time and didn't really have to money to buy one either. Eventually this got me into a 3 month job (sabbatical from my regular job) to develop a prototype on the iPad for a startup.
Not quite, the iPad gig was on OS X using Xcode (ugh!).
My first experience developing on iOS was SSH-ing into my jailbroken iPhone. Here are my notes on setting up the development environment but these are old by now and very probably not relevant anymore: https://www.dropbox.com/s/naq7763aximu8cx/iphone.org
If you are really interested I have a tarball with source and Makefile for you but it won't compile on recent toolchains I guess. (Also a bit of googling will get you examples as well.)
This is all thanks to saurik (who replied elsewhere in this thread) and others in the jailbreak community.
Also a lot of apps on Cydia were written using the GCC toolchain (at least initially, I'm not really up-to-date anymore).
