Apple officially released iOS 4.3 yesterday for the iPad (and iPhone/iPod Touch), with this release being quite similar to the GoldMaster version of iOS 4.3 which was successfully jailbroken.
Currently, the jailbreak is tethered only, meaning that a reboot of your iPad will require the jailbreak to be reapplied. Your best option is to stick with your untethered iPad jailbreak in iOS 4.2.1 via greenpois0n or PwnageTool 4.2 which addresses iBooks issues.
The kernel based greenpois0n RC5 and RC 6 exploit used for an untethered iOS 4.2.1 iPad jailbreak has been closed in iOS 4.3, likely leading to the use of SHAtter assuming the exploit hasn't been burned.
I myself am not a fan of a tethered jailbreak when my iPad is just fine running iOS 4.2.1 in an untethered jailbreak state. For a major update it would be difficult to wait for an untethered jailbreak for iOS 5 on my iPad...I would be willing to drop iOS 4.3 with a "more conveninent" jailbreak to apply an iOS 5 exploit.
This being said, I don't see the sense in writing a detailed "how to" when RedmondPie has already done this to apply a tethered jailbreak to iOS 4.3 via PwnageTool...but I'm gonna pass for now!
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