After wrestling with installing linux on Eee PC via a USB Linux distribution, I figured that it is a good idea to evaluate the various Linux distributions that work from a USB thumb drive. Unfortunately (or fortunately for me), Gary Sims of Linux.com already did it for me. He concludes

Of the two mini distros, I found DSL more useful because of the neater user interface and simpler install process. If you're looking for a complete Linux desktop on a USB flash disk, then Mandriva Flash is the clear winner. But if you don't want to spend money for your operating system, then you should consider Pendrivelinux.

For more details on how he evaluated the others, jump to the full article.