I tried installing Fedora 8 on my portable USB HDD. Didn't have any issues during the installation, but I am not able to boot from it. I have configured my BIOS to boot from USB Hard Disk but no luck
My computer goes on to boot Windows XP on the internal hard disk. I also tried it on a computer at work, but all I got was a blank screen when I selected to boot from the USB hard drive.
I wish it had worked.