Myself, I haven’t tired this, but it looks cool! Portable applications are just applications that store all your preferences and related files together. It could be on a USB drive, Zip disk or iPod. Perfect for taking your bookmarks, mail and setting with you when you go.
Sounds like a great idea to me. Use portable Thunderbird and you’ll always have your inbox with you. Use portable Firefox and have your bookmarks and your setting with you at all times. At the library, school, hotel or moms house!
The applications just run off your external media and save all program files there too.
There aren’t a whole lot of portable applications just yet, but I think they could be big. So far Firefox, Thunderbird, Cyberduck (ftp), Trillian Anywhere (IM) and Adium (IM) are a few available.