As you know Apple has released the new firmware update of iOS 4.3.4 to fix the all recent discovered untethered jailbreak exploits and the most awaited Safari exploit based PDF jailbreak which was recently released by Comex in the update version JailbreakMe 3.0. The update of iOS 4.3.4 is expected sometime before the launch of JailbreakMe because the jailbreak leaked at the time of launch and all iOS jailbreak developer believes that Apple will fix it quickly. So finally they released the iOS 4.3.4 yesterday night and at the first place it is only expected that it comes up as a killer of JailbreakMe but later the developer of untether exploit announced that his jailbreak exploit was also fixed in this update by Apple. i0n1c the author of untether exploit which was uses in iPhone Dev Team Tools tweets on his official twitter account that not to expect the iOS 4.3.4 untethered jailbreak anytime soon in near future.
So according to the i0n1c tweet there is no more untether jailbreak exploit in latest iOS 4.3.4, So many developers along with US warned users many time not to update their devices to the updated version of iOS because there is no jailbreak tool available to provide untether on iOS 4.3.4, but still we have a limera1n exploit of geohot which can easily jailbreak the iOS 4.3.4 but only tethered, means you have to connect your device to computer every time on boot.