I have a LiveUSB of Xubuntu 11.04 that I used for the installation onto my HD a while back. It seems to boot and run fine in Live ('Try') mode, so I'm perfectly fine with keeping it around 'just in case,' or as a handy way to carry a personal desktop environment around and just boot off that if I'm using a different computer.

But then I wondered if there is a 'just in case' where I might want something different - ie, would I be better off with a Lubuntu LiveUSB or one from Slax, both of which would probably boot/run faster if for some reason I had to use/fix an old or broken machine? I think the most common situations would be either a "Get files from Windows, throw a small 'Buntu install on there for backup" -type thing (like when I'm helping fix someone's computer), or a "Crap, I just broke my computer and I really need to keep doing x."

Other considerations:
1) I probably want to use FAT, so that I can keep using the USB for it's usual purpose - moving files between Windows/Mac computers.
2) I will be using a 2GB flashdrive unless I pick up an 8GB in the near future.
3) I also have a 500GB external drive for backup and extra ISOs, and will probably put an install of Xubuntu on a 20GB partition (which means I should probably go with something superlightweight on the flash drive, if I can just use the 'big guy' for serious installs.