Short answer, after a long time spent trying: NO.
I've been tinkering with USB memory sticks with Fedora9, Mandriva, Ubuntu, and Knoppix. I could get all except Knoppix to boot, but within a couple of days at most, they would develop one or another form of indigestion that dropped me to the bash: shell with the message
Bug in initramfs /init detected. Dropping you to shell. Good Luck!
And each time, that was it.
I wonder if there's anything that can be done from that point. If there is, I've not found it.
"Exit" brings up a Kernel Panic. ./init brings up an error.
The good news is that Fedora 9 and the one-step install is easy to do. But after an hour or two setting up the stuff I want to be "portable", it's a pain when it dies soon after. There doesn't seem to be a "repair" or an "update" or an "install but keep existing user settings" option.
I'd be happy if I could boot from the CD, and use the memory stick as a "Home" folder, which would hopefully avoid the problem, but I've not found a way to do that. A CDROM boot can see the pendrive but not the Home etc folder on it.
So I carry my laptop with me, rather than just a memory stick. I can't rely on the memory stick thing working when I need it.