I'm trying to setup some Xen stuff, and made 4 images, exactly the same, based on the Ubuntu hardy 64 bit system I'm running everything on.
I literally made the images with a bash loop, and they are all exactly the same, named xen{1,2,3,4}.
1, 2, and 3 start just fine, but 4 hangs on waiting for root file system.
Just a stab in the dark, but have you ran out of loop devices? run "cat /proc/diskstats" to see how many loop devices your kernel can use.
It was actually in the logs for the xen-create-image command. The disk image didn't get created properly since it was already mounted. I must have CTRL+C'd something and not umount'd the disk. umounting and remaking the domain fixed the problem.