I'm using mkinitrd-5.0.32-1 (FC-5 with all updates) I have my FC installation on an external USB drive (which I boot from) and I had to add withusb=yes in mkinitrd file to allow it to include usb drivers in the initrd. Otherwise I get a panic during boot where it can't find root fs. It would be nice if the usb-storage stuff could be included by default when the root or boot device is on usb???