updated 01:05 pm EST, Fri January 20, 2012
Absinthe ready to go
(Update: Windows too) The promised iPhone 4S and iPad 2 untethered jailbreak has been posted as of Friday. Absinthe lets Mac users crack iOS 5 on the modern Apple hardware to run Cydia as well as other unsigned apps. Demand is such that the main host, greenpois0n, is currently having trouble; Chronic Dev Team contributor Josh Hill warned that the jailbreak might not run at first, since it's dependent on reaching the greenpois0n site.
As with all jailbreaks, the code isn't guaranteed to work and carries the risk of bricking the device if something goes wrong. Some are already reporting that it purges the camera roll, so those without backups of recent photos are advised to hold off.
Linux and Windows users will also have to wait for ports of Absinthe that don't yet have a release window. iPhone Dev Team is promising an interim command-line jailbreak tool.
Jailbreaks for A5-based iOS devices have been some of the most elusive. Whether intentional or not on Apple's part, the more recent processors have been harder to crack and have regularly been excluded from jailbreaks for nearly a year. A similar pattern might emerge if Apple moves to a likely, though unconfirmed, A6 chip for 2012-era iPads and iPhones.
Update: The jailbreak is now available for Windows users.