Write .iso to USB on Mountain Lion
did you try: 

hdiutil convert -format UDRW -o ~/path/to/target.img ~/path/to/target.iso


after that unmount using:

diskutil unmountDisk /dev/diskX


(X is the disknumber of your usb device)

Now just burn it using dd

sudo dd if=/path/to/target.img of=/dev/rdiskN bs=1m