I have this problem. I was experimenting if I could use a memory card (SDHC) as an USB drive for all intents and purposes, and when I put the card in an USB card reader, I can use it just like regular USB stick and it also shows up in the BBS popup menu as an USB stick. When I tried to create an installation media out of it like this:

sudo dd if=/path/to/image of=/dev/sdb

And tried to boot from it, simply nothing happened. Cursor blinked a couple times, and jumped to the GRUB of my pre-existing GNU/Linux installation. What am I missing here? Is this not doable?

I tried this with Xubuntu 12.04 and ArchLinux, by the way. I have also tried UNetBootIn instead of dd. Nothing happened differently.