Today a hacker team known as "greenpois0n" released the first working untethered Jailbreak for Apple devices powered by the A5 processor, namely the iPhone 4S and iPad 2. While the practice is officially discouraged by Apple and may cause some unintended consequences if you don't know what you are doing, jailbreaking is entirely legal and essentially enables smartphone and tablet owners to customize their devices and run unsanctioned software from third-party app stores such as Cydia.
The practice is not uncommon among Android users either, who often turn to rooting their devices in order to load the latest version or a customized build of the OS rather than wait for an official update -- which sometimes never comes, unfortunately.
But then there's the other side of the coin: despite the benefits of jailbreaking, some people just can't be bothered with the whole backup-upgrade-jailbreak-restore cycle every time something better comes out. I used to jailbreak my iPhone but don't anymore after realizing I rarely even used unofficial apps.
So our question for those of you with smartphones is, do you jailbreak or root your device? If so, tell us about the custom ROMs and 'unofficial' apps you run, as well as the tweaks you can't live without. Also, has this caused any security or instability issues for you?