ISO="ubuntu-12.04.2-desktop-amd64.iso"
IMG="ubuntu-12.04.2-desktop-amd64.img"
DISK=/dev/disk1
hdiutil convert -format UDRW -o "${IMG}" "${ISO}"
diskutil list
diskutil unmountDisk "${DISK}"
#ridsk instead of disk can be faster
dd if="${IMG}" of=/dev/rdisk1 bs=1m
diskutil eject "${DISK}"