Here’s an interesting site:
A portable app is a computer program that you can carry around with you on a portable device and use on any Windows computer. When your USB thumbdrive, portable hard drive, iPod or other portable device is plugged in, you have access to your software and personal data just as you would on your own PC. And when you unplug, none of your personal data is left behind.
There are portable versions of most of the current Open Source apps – Firefox, GAIM, Thunderbird, Abiword, OpenOffice…
Portable apps are a limited solution. I think that we need Portable Environment