The Dev Team lists 3 different scenarios for jailbreakers to be aware of:
- A4 devices and 3GS will always be downgradable (and jailbreakable) due to limera1n. The tethered iOS6 jailbreak for those devices (and untethered for old-bootrom 3GS) will be out when Cydia and other important pieces are all working properly
- iPad2 owners who have both 4.x blobs and 5.x blobs will always be able to downgrade to those versions, even once you come up to 6.0 and the 5.1.1 window closes (don’t do that yet though!). You need both 4.x and 5.x blobs to qualify for the downgrade even if you only wish to downgrade to 5.x
- iPad3, iPhone 4S (and iPad2 owners who don’t satisfy #2) will always be able to RE-restore the current 5.x OS that’s already on their device. So if you’re at 5.1.1 when the window closes (and you’ve saved your blobs), you’ll always be able to RE-restore to 5.1.1 again. This makes the 5.1.1 jailbreak a lot less fragile — you don’t have to worry about messing up your install with funky extensions or getting into a boot loop, because you can always RE-restore from 5.1.1 to 5.1.1 again (or from 5.0.1 to 5.0.1 again, etc). But once you fall off the 5.x train by restoring to 6.x, you’ll be stuck there until the next jailbreak.
Translation, for the A4 devices (i.e. iPhone 4 and Original iPad) you are good, the limera1n exploit will provide an iOS 6 tethered jailbreak very soon.
For A5 devices (iPad 2), if you have blobs from 4.x or 5.x you will always be able to downgrade.
Finally, for the iPad 3, iPhone 4S and iPad 2 owners without blocks saved, you will be able to RE-Restore your device to iOS 5.1.1 with the latest version of RedSn0w.
Clear as mud?