Yesterday when the Siyah kernel developer updated 3.1RC6 there was a bug introduced that was bricking devices when the user performed a factory reset. Nobody is sure if it is a hard brick or a soft brick but at this point in time, no one has been able to un-brick their device.
In my guides I am only using the 3.0.1 stable version, so it is not a problem for those using that one. But if you are using a different source than this blog any 3.1RC6 version older than today is suspect. You can find more info on the official thread.