Have you installed "Siri" from Cydia? You may not be able to do untethered jailbreak!

  Last evening iH8sn0w made an interesting and very worrying statement for those who tested the ports for Siri launched in Cydia in recent weeks. It seems that if you installed such a "Siri" from Cydia, you modified certain files from iOS 5 and the future untethered jailbreak solution could be incompatible with your terminal. Now if you can restore the problem can be solved very simply because you rewrite the files, but if you can't restore you might have some problems.

   iH8sn0w says that H1Siri is one of the problem ports and that any other port that is over 150MB in size is a problem. chpwn confirmed what iH8sn0w said, so unfortunately if you have installed H1Siri you may have problems using the future untethered jailbreak solution. For now, take everything with a grain of salt because it is not known if everything we are being told now will happen or not, but be prepared to do a restore in case the solution is launched and you cannot use it.