If you’re a Linux big fan,you’d have a couple of Linux distributions in your computer.And there is a free software called MultiBoot can make them all bootable in one liveusb,so that you won’t worry about how boring to burn them each.
MultiBoot will enable you to make a liveusb to do everything,ideal for exploring different Linux distributions without installing on your PC and does so fluid;or to install the linux distribution your choice on your PC much faster than via a LiveCD with fast USB 2.0/3.0 ports.Essential on the entire current range of netbooks that have no CD.Ideal for any Geek, anyone doing maintenance,your USB key with you always, and ready to be used as mobile with your friends in a cafe.

MultiBoot supports almost Linux distributions,such as Ubuntu,Open Suse,fedora,CentOS,etc.You can see the list current supported Linux distributions from http://liveusb.info/dotclear/index.php?category/OS-Supportes;And the system logos:http://liveusb.info/
Install and Use MultiBoot

Download MultiBoot from:http://liveusb.info/dotclear/index.php?category/Installation.Extract the package and run the script.It’ll take a few minutes to download required packages and install them.

Once installation finish,you can lunch from Applications->Accessories->Multi System.Drag and drop your iso files on this window and that’s all:

Example startup screen with obtemu grub2: