Version 0.9.10b7 of redsn0w adds a collection of useful features: It finally implements the corona-A5 jailbreak for iPhone4S and iPad2 devices still at 5.0.1. It can also re-install that jailbreak for those who accidentally uninstalled the untether. When stitching an IPSW, it can now grab your blobs directly from Cydia. It now shows a lot more info about your device (for instance, whether your iPhone3G has the vulnerable baseband boot loader, or whether your iPhone3GS has the old exploitable bootrom. (And the next new feature to be added will be built-in restore support, to provide an alternative to iTunes restores.)
Previously you needed to use Absinthe to jailbreak the iPhone 4S and iPad 2.
You can download the new version of RedSn0w from here.