I've tried to unbrieck my Acer iconia
But the system blocked after executing the command :
dd if=/sdcard/system.img of=/dev/block/mmcblk0p3

I have no other solution than rebooting ... But sometimes, I didn't wait enough because I had the Android screen wich ask a system (the android robot with the !).

How many I have to wait to be sure that the command is finished ?

Thanx a lot !