Oh, and Leopard too.
What a title. I recently needed to use G-Parted, but didn't have any blank disc's laying around, and the method they describe on the gparted wiki to do this with a USB disk doesn't work on OSX. So, I used DD.
Open up terminal (from Applications/Utilities or use Spotlight) and type what follows substituting as necessary. My USB device was located at /dev/disk3. You can find the device name in Disk Utility by right-clicking on the device, and choosing 'information'.
THIS WILL OVERWRITE WHATEVER'S ON THE DISK.
And voila, you have a read-only replica of the iso on your usb device. Please note the emphasis on read-only in the case of an ISO.
To see a progress bar (of sorts), open up a new terminal window and type the following
I originally got the progress bit from here, but changed it to work with OSX.