From Penlinux.com,

Now you can take your Linux desktop with you anywhere! PenLinux.com sells usb flash drives with Ubuntu Linux pre-installed. All you do is plug it in to any computer running Windows (Windows 98 and up), click an icon, and your Windows desktop turns into your Ubuntu Linux desktop, and when you’re done, switch back to Windows, without a single reboot!

Why would I want one?
- Size. Take your desktop anywhere (a friend’s house, the library, school, work, etc)… it fits in your pocket!
- It uses Linux technology.
- It’s a great way to learn linux on your PC without actually installing it on your hard drive.
- It doesn’t make changes to the host PC.
- Unlike a LiveCD, our usb drives allow you to save and install software that will still be there on your next boot.

You just need decent speed computer with good memory size to run without any hickups. Ubuntu Linux in your finger tip.