Apple will no longer allow users to update or restore an iOS device to iOS 4.3.3. The signing window for 4.3.3 has been closed, meaning that you can no longer restore a device to 4.3.3 in iTunes without previously saved SHSH blobs from that firmware.
This news is important for jailbreakers that are either considering using JailbreakMe on iOS 4.3.3, or those that may have possibly upgraded to an iOS 5 beta without saving their blobs. The recently released iOS 4.3.4 kills the untethered jailbreak that was previously offered in iOS 4.3.x, so 4.3.3 is the most up to date firmware that offers an untethered jailbreak.