The Chronic Dev Team has released the greenpois0n untethered jailbreak
for iOS 4.2.1. It took an extra 48 hours for the jailbreak to be released for those using Windows systems (meaning, most of us), but that's now here as well.
An untethered jailbreak means you can now boot your iDevice without having to have it tethered to a PC at the same time. The greenpois0n jailbreak now runs the gamut of Linux, Mac, and Windows based systems. However, just as the jailbreak arrives, there are rumors that Apple will be announcing iOS 4.3 any second now. As they just released iOS 4.3 beta 3 last week, we know it's coming soon, but as with any new Apple product or platform version, the question is when.
Once that happens, we'll again be waiting for a jailbreak so we can upgrade to the new iOS (right, as we assume you don't mistakenly upgrade before a jailbreak comes live, and thus lose all your jailbroken goodness). Jailbreaking allows the installation of software that Apple
doesn't allow in the App Store, including some that allows end users to have a useful Lock Screen, for example