It's been a long time coming. We've been waiting for an untethered iOS 4.2 jailbreak for quite a few months now. It will be nice to finally power up your iDevice without having to connect your device to the computer each time. Currently, it's Mac only.
We haven't tested it out yet, but it's been reported that the release was rushed. Our advice is to wait a bit and see what the comments are from those who install it early. Still, if you are willing to try it out, head on over to GreenPois0n.com and download.
Once again, we haven't tested it out, we'd suggest waiting until you see what others experience before going ahead with the JB.