You should read the latest on hacking MicroSD cards by Bunnie Studios (http://www.bunniestudios.com/blog/?p=3554).
Some points to consider:
- Every card has a ARM microcontroller;
- Flash is usually bad, but it doesn’t go to waste. a 16GB card with 80% bad flash can be sold as a 2GB one;
- Remember number 1? It can allow arbitrary code execution.
Interested on reading more?
This is the whole write up – http://bunniefoo.com/bunnie/sdcard-30c3-pub.pdf – and here’s the whole video. Enjoy!