The latest version of iOS 5.1 is already jailbroken thanks to the iPhone Dev Team’s newest release of Redsn0w. The jailbreak is tethered however, meaning that each time the iOS device is rebooted it will need to be connected to a computer running redsn0w for boot assistance. iBooks doesn’t yet work either, but an update is expected to resolve that issue shortly. If neither of these two things bother you, grab the jailbreak and enjoy.
Redsn0w 0.9.10b6 works with the following devices running iOS 5.1: iPhone 3GS, iPhone 4 CDMA & GSM, iPod touch 2nd, 3rd, & 4th gen, iPad 1. Not supported are any A5 based hardware, including iPhone 4S, iPad 2, and iPad 3.