I keep a certain set of bookmarks and shortcuts, not to mention browser extensions and other customizations, on my primary computer. I found it very inconvenient to attempt to do things at home without bringing my work laptop home, which I don't really want to do. I also found that I had to install and maintain several instant messaging programs at home as well as work... that got to be a pain.
A while back I noticed someone was making FireFox portable. I got interested, but I didn't think the package was ready. But with FireFox release 1.5, I finally got truly comfortable with my customizations. I decided to undertake transporting my settings.
There's quite a few portable apps out there now. Most are open source, and almost all of them are free. Basically, the idea is to be able to carry your own applications and settings with you on a USB or other removable storage, and leave no junk behind when you disconnect. The OpenOffice suite is now portable, so I may upgrade to a 256 MB drive and use AbiWord for routine word processing and OpenOffice for all the other things.
So far I'm only carrying my own web browser and instant message software on my USB keychain. So far, I've got FireFox (with all my settings and bookmarks) and GAIM (my instant messenger), as well as FileZilla (my FTP client of choice) and AbiWord (word processor). I'm planning on adding Skype, compression utilities, spyware removal and probably an antivirus program. This would bring me close to 100 MB on my 128 MB keychain. If I get good enough at it, I may post a how-to entry.
If you are interested in portable apps, check out these web sites: