Dev Team has announced that Greenpois0n will be updated within the next few days to allow for 4.2.1 to be Jailbroken. As of right now, the Jailbreak will be tethered for all 4th gen based devices (iPhone3GS w/ new bootrom, iPhone4, iPad, iPodTouch3&4) but Comex is hard at work creating a userland exploit to untether 4.2.1. Word is that this untethering will require 4.1 SHSH Blobs. If you have not saved your blobs yet, even if you are not currently Jailbroken and/or not currently using iOS 4.1, you can go ahead and use TinyUmbrella to save them. However, since 4.2.1 was just released, Apple will stop signing 4.1 SHSH blobs very soon (any minute really) and once that happens, you are out of luck!