It might be very rare (actually it happened to me only once, few months ago, while doing "dev work" and I had no RS232 cable, I locked myself out because of a bad rom flashing) but if your device seems dead and refuses to boot to recovery using the bottom located pinhole as trigger to enter recovery (see CWM or TWRP threads for more infos about entering recovery) don't be afraid because, unless you suffer of an hardware failure, you will be able to unbrick it using this MicroSD rescue method.

mmcinfo
fatload mmc 0 0x82000000 u-boot.bin
sf probe 2
sf erase 0 60000
sf write 0x82000000 0 60000
sf erase 0x100000 0x8000
reset