Largely sourced from: this
Convert the ISO to its Imagable, non-optical-media counterpart
hdiutil convert -format UDRW -o output/path/output.img path/to/original.iso
Unmount the destination USB key
diskutil unmountDisk /dev/diskX # where X is the node number of the USB drive
DD the image out (the bs=1m is important!)
sudo dd if=output/path/output.img of=/dev/diskX bs=1m
Eject the USB drive before pulling it out to use it on the system you need to boot it on
diskutil eject /dev/diskX
I got tired of having to hunt this down; i use it infrequently enough that it I always forget the details, but every time I need it I end up finding it somewhere else…
Most recently I needed this trick to install the new XBMCbuntu Eden on my media center. My old release was starting to show its age a little; it was ugly, bloated, and buggy as hell. Eden is already more awesome. Read: AIRPLAY!!!!
For the record, I have used unetbootin, both this time and in the past, with mixed results. Typically if i did it from a PC, it worked. The Linux and Mac versions of the app have never worked as promised for me, this time was no exception.