Supposedly if you are a dev (or pirate) and acquire 4.2b3 IPSW and use redsn0w 0.9.7 b6 (just released), you can have an untethered 4.2.1 jailbreak. I haven't tested it myself because I am sticking with 4.1 limera1n. And it's still in beta form, but it might be worth trying for those who are impatient. Mac users only at the moment. No windows version.