UNetbootin stands for "Universal Netboot Installer," and essentially allows you to easily create a bootable USB with many Linux distributions. For those who've never tried, creating a bootable USB can actually be quite the hassle, so UNetbootin makes it much, much easier.
If you want to absolutely go hands free on a bootable USB, you can select from several common linux distributions, such as Ubuntu, Damn Small Linux, Puppy Linux, FreeBSD, Fedora, Gentoo, MEPIS, Mandriva, Slax, Frugalware, and many more. When you select one, you can then select the version (such as "8.10 live" or "8.04 install" for Ubuntu), or just pick to go with the Latest version, in which case, UNetbootin will check and download the latest released version. After you choose your distro, version, and select the USB drive, UNetbootin will automatically download the specified ISO, and make it into a bootable USB, meaning that you can walk away from your computer, then come back a few hours later (maybe less, if you chose a distro like Damn Small Linux) and have a fully functioning bootable USB device, no hassle.
Or if you already have your ISO and want to burn it, there's an option for that as well. Just show UNetbootin where your ISO is, select your USB drive, then hit "OK", and it creates a bootable USB from the ISO of your choice. It really is just that easy.
OR if you REALLY know what you're doing, you have the option of selecting the Kernel and the Initrd, and specifying Options.
Lastly comes the drive selection. UNetbootin is defaultly set to only display USB drives, but you can (if you dare) let it "Show all drives", but remember that if you accidentally choose your C:\ drive (or whatever drive your Windows is installed), you could screw up your Master Boot Record, and unless you know how to fix that.....well, just don't do it.
UNetbootin is a very, very handy program for those who want a bootable USB drive without any hassle. The very nicest part about UNetbootin is that you don't have to format your USB drive. That means that you can have your apps on the USB, then UNetbootin a Linux distro, and all your apps will be completely uneffected. All it does is just copy the needed Linux files from the ISO, set up a Syslinux boot menu, and edit the MBR on the USB drive. So if you don't like your Linux distribution, just delete the files. (Of course, your MBR would still stay changed, and I'm not smart enough to tell you what to do about that...) Probably the best part about it is that it is portable, and it is fairly small (around 3.5mb).
It's a very, very handy program if you don't have an available CD drive, or if you just prefer USB. There's also specialized versions of UNetbootin such as Auto Super Grub Disk, EasyPeasy, EeePCLinuxOS, xPUD, and FUSBi. EasyPeasy and EeePCLinuxOS are built specifically for the purpose of installing Linux to Netbooks, which makes UNetbootin a Netbook's best friend. (At first, I thought it was actually short for "Universal Netbook Installer" :P)
*My apologies to all smart Linux-people, if I misused a phrase here or there, or got something completely wrong. Feel free to correct me.
Visit UNetbootin website for download