It is possible that flashing ICS kernels can brick your device. GB kernels were safe, but not so for ICS. It occurs if a bad kernel issues a certain erase method, whereby your device will lose all ability to boot thereafter. This problem mainly effects the Galaxy Note, but it is possible certain GS2's can also be affected (depending on what chip you have and what kernel you flash) Good old Chainfire has written an app that can detect if your GS2's chip to see if it can be affected or not. The app can be downloaded in his Brick Bug Thread According to this app, mine is affected! I will now need to be very careful what kernels I flash in future. I will now only ever flash Siyah, and I will also make sure any ROMs I flash only come with Chainfire or Siyah kernels.