When iOS 5.1 was newly released, there were warnings fro jailbreakers, advising them against updating their iPhones to iOS 5.1 until a jailbreak for iOS 5.1 would be available.
Updating to iOS 5.1 would have dismantled all the jailbreak tweaks in an iPhone. And downgrading back to iOS 5.0.1 was also not possible because Apple has stopped signing it, immediately after releasing iOS 5.1.
Now a similar warning has to be issued to jailbreakers due to recently released iOS 5.1.1.
The new update to iOS does not appear to bring any new features. However, it does include a handful of bug fixes and other improvements.
Although, A4 devices running the new firmware can be jailbroken, that does not mean people with jailbroken iPhone should update. Those of who have an A5X device should stay away from the new update.
Hacker MuscleNerd has sent out a warning via Twitter, telling jailbreakers with an iPad 2, a new iPad or an iPhone 4S to stay away from the update. Hacker pod2g is making great progress with the iOS 5.1 jailbreak, and upgrading to 5.1.1 could ruin your chances of using it. pod2g is testing a jailbreak tweak on his iPhone 4.
A4 device owners are welcome to upgrade at their own risk. iOS 5.1.1 can be jailbroken on older devices. However, currently remember that it is a tethered hack.
Source: iDownload Blog