With iOS 4.2.1 being released to the masses today, here's a couple tips for jailbreakers. If you're on iOS 4.1 and jailbroken, by this point you should know how to save your SHSH blobs via TinyUmbrella or Cydia.
As of right now, most jailbreak methods that work on iOS 4.2.1 are pretty hairy. I highly suggest waiting to upgrade for the official tools, but if you feel the need to give it a try right now, I've put up an iOS 4.2.1 jailbreak guide in our forums. Ask questions, give answers, and help eachother out. You can always visit our general jailbreak forum and post other questions and find answers about other topics as well.
Whatever you decide to do, let us know how it works for you!
Update: The Dev-Team has updated their blog giving everyone a bit more information about iOS 4.2.1 and how it'll affect all devices. Make sure you read it and heed their warnings when updating. It's looking like older devices will have an easy upgrade route to a jailbreakable 4.2.1. Newer devices are (as of now) tethered. I urge anyone who wants to upgrade to weigh their options before deciding to upgrade. You may lose your jailbreak or be tethered. A tethered jailbreak basically means if your phone battery dies or you need to reboot, you'll need to be connected to a computer to enter into a jailbreak state again. They're somewhat of a pain and I'd suggest waiting for an untethered jailbreak. You probably won't be waiting long. Until then, make sure you have your 4.1 SHSH blobs saved via Cydia or TinyUmbrella!