The nice way to get a progress bar while making a bootable USB drive on a mac is:
pv -ptre /path/to/some.iso | dd of=/dev/diskX bs=1m
pv does the progress bar magic, you may need to install pv first:
sudo port install pv
the parameters to dd: of, the out file, in this case the USB device and bs will make sure things move a bit faster.