I did not bring my ancient CD/DVD external disk with me to Costa Rica. Consequently, updating all my Linux distributions left me with creating bootable USB sticks. For the three distros that I need to upgrade, I put each distro on a separate USB stick. After rebuilding my netbook, I discovered a better way.
Creating USB sticks for each distribution of Linux required more USB sticks than I owned. I was only using a fraction of the space on the space available on a USB stick. There had to be a better and easier solution.
After spending a bit of time with Google search, I found MultiSystem. Yes, the site is in French, but there is a Google Translate selection in the right column. The site offers a number of different installation options. For automatic update notification, I prefer to add the download site to my package manager repository. The instructions on their site has a number of typos. A better set of instructions can be found at Linux Tech Crunch. To the best my knowledge, there is only a Debian package, no RPM version.
Since I am using Linux Mint 12.1, MultiSystem automatically uses GRUB2, and builds its own grub.cfg file. MultiSystem also supports GRUB, GRUB4DOS, and SysLinux. It all depends on the bootloader for your system. GRUB2 installs to the MBR, and it worked fine on my netbook. Just select the USB stick you want to use, and click the confirm button.
The main menu is the administration menu for MultiSystem. The size of your USB stick is the only limit to the number of Live/Install distributions that you can add to the list. There are Live/Install distros, such as Megia and PartedMagic, that MultiSystem does not support. There are some that do not boot correctly, such as PCLinuxOS.
MultiSystem installs from an .iso image that you have downloaded. I actually downloaded images to an external USB drive and installed them from that drive. To make life easy, MultiLinux contains a list of Live/Install images available. Just click the download button and select the distro that you wish to install. Multisystem redirects to the distros download page, where you can download the version that you want. This is the time consuming part, the rest is easy.
From the install dialog, at the bottom of the window, select the iso image that you want to install on the USB stick. You need to double-click the file to select it. The iso has to appear in the left window. After you click the Create button, Multisystem opens a shell dialog window. You just need to enter your password, and it does the rest.
MultiSystem allows you to test your work in either QEMU or VirtualBox. With MultiSystem, the first item on the menu is always the default. However, you can use the move errors to change the order of the boot screen. MultiSystem updates the GRUB2 after each move, so this can be a bit time consuming.
Some distributions allow you to create a persistent Live/Install version. Knoppix did it as part of the install process. For other Live/Install versions that support persistent versions, MultiSystem has an option to create one. The persistent version always appears as a separate menu item.
In my opinion, MultiSystem is the best tool for exploring and installing multiple versions of Linux. I only wish that I had a USB stick with more capacity. A 4gig USB stick is just to limiting. Of course, I just may build another USB stick for other distros.