It's been out for a little while now... As iPhone Dev Team puts it: The untether is for iOS 5.0.1 on iPhone3GS, iPhone4, iPhone4-CDMA, iPad1, iPod touch 3G, iPod touch 4G If you have one of those devices and are not on 5.0.1 yet, update now! The SHSH window is still open for 5.0.1 If you unlock via ultrasn0w or gevey, make sure you only get to 5.0.1 via a custom IPSW! See the guides at places like iClarified.com if you dont know how. Once youre at 5.0.1, use the latest redsn0w 0.9.10 to both jailbreak and untether.
If youre already at 5.0.1 with a tethered jailbreak, you have two choices: either run redsn0w 0.9.10 over your current jailbreak (deselect Install Cydia if you do that), or install the Cydia package prepared by the chronic devteam. The patches are the same regardless of which you choose.
Some of you are using a hybrid 5.0/5.0.1 configuration. If so, do not attempt to install this untether over that setup! You will most likely get into a reboot cycle. Do a sync and fresh restore to 5.0.1 then install the jailbreak + untether.
Check out the iPhone Forums Jailbreak section for info!