With this version, Apple has only patched the PDF exploit used by jailbreakme.com 3.0. Though it is a remotely exploitable security issue, another major reason for issuing this update is to stop jailbreakers. They’ve already released a tethered jailbreak for 4.3.4, but there’s not really any point to doing it. 4.3.3 + jailbreakme.com + Cydia’s PDF Patcher 2 will get you an untethered jailbreak with the PDF exploit patched. As always, unlockers should be especially careful with new iOS versions and baseband upgrades.