The Dev Team has released an update to the jailbreak tool, RedSn0w, with support for a tethered jailbreak on iOS 4.3.4. Apple released 4.3.4 yesterday to combat the PDF vulnerability uncovered in the latest version of JailbreakMe.
JailbreakMe users are advised to stay with the untethered jailbreak that the web-based tool provides on iOS 4.3.3, and not upgrade to 4.3.4.