Here are the basic steps for how to get 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 don’t know how. Once you’re at 5.0.1, use the latest redsn0w 0.9.10 to both jailbreak and untether.
If you’re 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.


Update #4: The b4 version of redsn0w incorporates the 5.0.1 fix for iBooks, and also for sporadic problems with launchctl. Thanks to @xvolks for merging the iBooks (sandbox) fix from @comex’s github into the overall corona untether from @pod2g! As usual, you can choose to install the fix either by re-running redsn0w over your existing jailbreak (de-select Cydia if you do that), or by installing the corona package from Cydia (it’s the same set of files no matter which way you choose).
TIP: If auto-detection fails and redsn0w tells you no identifying data was found, you can always pre-select the appropriate 5.0.1 IPSW using “Extras->Select IPSW”.