@pod2g has been working very hard on an untether exploit he found a few weeks ago. He recently decided to give the exploit to the Chronic Dev Team an the iPhone Dev Team to release it for non-A5 devices. Because the new A5 processor, used in both the iPad 2 and the iPhone 4S, does not apply to GeoHot’s limera1n exploit, it is much harder to jailbreak those devices. @pod2g is still working on a jailbreak for the remaining two devices.
As always, you should not update your device if a new firmware is available because the untether exploit will most likely be patched.