Round piece of plastic which can hold some information in electronic format.
Also can be used as coaster for coffee cup.
With a little work from an old 'Make' article you can also use it as a target for shotgun practice---cheaper than clay pigeons and they have that 'ooh shiny thing' going for them.
Hmm, burning a bootable ISO image to a USB stick seems more reasonable from time to time.
Not all Linux distributions have ISOs ready for USB-usage. Some of them are still sticking to CD as media.
Is there anything that Unetbootin won't work on?
Unetbootin can be slow since it unpacks the ISO and copies all the files over to the USB drive. Also, this will always grab the latest for the distro's servers.
YUMI is OK if you spend the time to download the distros ahead of time and store them all on your USB key. NetBoot is good if you want to get a distro you haven't downloaded yet. That way you have a lot more distros available than can fit on your thumb drive. The downside is that you have to download them every time you install them.
I expected to see Arch Linux in the list. Go figure.