Got an iOS device running 4.2.1 that's in dire need of an untethered jailbreak? Good news; the Chronic Dev Team has released a new solution, GreenPois0n, promising an untethered jailbreak suitable for Mac, Linux or Windows users, and opening up your iPhone, iPad or iPod touch to the joys of the Cydia unofficial app store.
Unfortunately, according to Chronic Dev Team member Joshua Hill, the exploit GreenPois0n uses has already been patched by Apple in iOS 4.3. That means there's only a limited amount of time to make the most of it, and it's unclear whether it resets the cat & mouse clock in the process.
Still, for the moment iOS 4.2.1 is where it's at, and GreenPois0n doesn't demand a jailbreak every time you power cycle your device. Let us know how you get on in the comments.